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Glossary of Terms

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Analog Communication

A communication format in which information is transmitted by modulating a continuous signal, such as a sound wave. Current TV and radio signals are analog, as are many telephone lines. See also Digital Communication


American Standard Code for Information Interchange. Standard 8 bit code used in data communications. Many files interchanged from one software program to another and from IBM to Mac formats go through translation into ASCII.


A type of two-way communication that occurs with a time delay, allowing participants to respond at their own convenience. Literally not synchronous, in other words, not at the same time. Example of an application of asynchronous communication is electronic bulletin board.

Asynchronous Transfer Mode (ATM)

Communication technology that uses high-bandwidth, low-delay transport technology, and multiplexing techniques. Through dedicated media connections it provides simultaneous transport of voice, video, and data signals more than 50 times faster than current technology. May be used in phone and computer networks of the future.

Audio Bridge

Specialized equipment that interconnects three or more telephone lines (usually operator assisted) to enable conference calls. The audioconferencing equipment needed to connect multiple sites can be provided by companies specializing in bridge services.


An electronic meeting in which participants in different locations use telephones or audioconferencing equipment to interactively communicate with each other in real time. The number of participants may be as small as 3 or as large as 100 or more.

Authoring Software/Tools

High level computer programs designed for use by non-programmers in the creation of computer-based training, interactive presentations, and multimedia. The commands are presented as simple terms, concepts, and icons. The authoring software translates these commands into the programming code needed by the computer and related hardware devices.

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Maximum frequency that can be used to transmit a communication signal without excessive distortion. Measured in Hertz or cycles per second. The more information contained in a signal, the more bandwidth it requires for distortion-free transmission.

Baud Rate

The transmission rate at which data flows between computers. The baud rate is roughly equivalent to the number of bits per second (bps).

Bit (binary digit)

The smallest unit of information a computer can use. A bit is represented as a "0" or a "1" (also "on" or "off"). A group of eight bits is called a byte. Bits are often used to measure the speed of digital transmission systems.


An academic and research computer network that stores and forwards messages sent between users. This system was a precursor to the Internet and its use today is limited.


Software that allows you to "surf " the Internet. Netscape, Mosaic, and Internet Explorer are examples of Web browsers. A browser provides an easy to use interface for accessing the information on the World Wide Web.

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Memory that holds copies of recently accessed data. Several Web browsers keep recently viewed pages in a cache so users can return to them quickly without suffering network delays.

Computer-Assisted Instruction (CAI)

See Computer-Based Training (CBT)


A type of satellite transmission with less path loss than other satellite standards such as Ku-band. C-band, however, requires a relatively large antenna. C-band frequencies are shared with terrestrial microwave transmissions, which can cause interference with weaker satellite signals in certain areas.


Two or more individuals connected to Internet have real-time text-based conversations by typing messages into their computer. Groups gather to chat about various subjects. As you type, everything you type is displayed to the other members of the chat group.


Coder/decoder equipment used to convert and compress analog video and audio signals into a digital format for transmission, then convert them back to analog signals upon reaching their destination.

Compact Disc (CD)

High density storage media based on a 4.75" reflective optical disc. Can hold up to 650,000,000 bytes of data, that is equivalent to 12,000 images or 200,000 pages of text. CDs may all look the same, but there are numerous standards for different applications. The most common are defined below.

Compact Disc-Interactive (CD-I)

Interactive multimedia platform developed for the consumer market by Philips. It is a proprietary version of the CD-ROM that delivers data, text, audio, stills, and video.

Compact Disc Read-Only Memory (CD-ROM)

Version of the CD that allows the information to be stored and retrieved. Once a CD-ROM is pressed, new data cannot be stored and the disc cannot be erased for reuse. Although CD-ROMs look like music discs, they can only be used with a computer equipped with a CD-ROM drive.

Compact Disc-Recordable (CD-R)

CD-ROM recording systems can be used to record data onto a compact disc-recordable like any other recordable media. However, they cannot be erased and re-recorded. For large-scale duplication of CD-ROMs, a pressing facility is preferred.

Compressed Video

A digital transmission process used to transmit a video signal. When the vast amount of information in a video transmission is compressed into a fraction of its former bandwidth by a codec, the resulting compressed video can be transmitted more economically and through existing phone lines. While compressed video requires less bandwidth, signal quality may be reduced. As a result, picture quality is generally not as good as full-motion video. Quick motions often appear somewhat blurred. This quality issue is becoming less of a concern as more and more playback systems for compressed video run at 30 frames per second.

Computer-Based Training (CBT)

An interactive instructional approach in which the computer, taking the place of an instructor, provides a series of stimuli to the student ranging from questions to be answered to choices or decisions to be made. The CBT then provides feedback based on the student's response.

Computer Conferencing

An ongoing computer conversation via text with others in different locations. Conferencing can be done in "real time," so that messages appear as they are being keyed, or it can be "asynchronous," which means the complete message is keyed and then stored for later use by the receiver or sender.

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Direct Broadcast Satellite


Digital Direct Satellite

Desktop Publishing

Software programs that enable the user to use a microcomputer and a laser or color printer to produce relatively high-quality publications.

Desktop Videoconferencing

Videoconferencing on a personal computer equipped with a fast Internet connection (at least 28.8 Kbps modem), a microphone, and a video camera . There can be two-way or multi-way video and audio depending upon the hardware and software of participants. Most appropriate for small groups or individuals. Not yet presently available in many parts of the country due to bandwidth and equipment limitations for this application.

Digital Communication

A communications format used with both electronic and light-based space systems that transmits audio, video, and data as bits ("1s" and "0s") of information. Codecs are used to convert traditional analog signals to digital format and back again. Digital technology also allows communications signals to be compressed for more efficient transmission.
See Analog Communication


An earthbound dish-shaped antenna used for receiving satellite signals. Also referred to as downlink dish and ground receiving dish.

Distance Communication

Use of telecommunication technology for the implementation of administrative activities such as meetings, focus group, or job interviews when the parties are located at two or more locations.

Distance Education

See Distance Learning. The term distance education is often used synonymously with distance learning. However, distance education typically refers to distributed learning resources in academic settings.

Distance Learning

A system and a process that connects learners with distributed learning resources. While distance learning takes a wide variety of forms, all distance learning is characterized by the following: 1) separation of place and/or time between instructor and learner, among learners, and/or between learners and learning resources, and 2) interaction between the learner and the instructor, among learners, and/or between learners and learning resources conducted through one or more media; use of electronic media is not necessarily required.


A procedure for transferring or retrieving a file from a distant computer. Opposite of uploading. Many Web sites have links to files such that you can simply click on the link and your browser will handle the downloading of the file(s) to your computer.

Duplex Video

Two-way video communication capable of simultaneous origination and reception.

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Earth Station

A ground-placed antenna used to transmit or receive signals to or from satellites, typically located in geostationary orbit.

Electronic Bulletin Boards

Information services that can be reached via computers connected by modem and/or Internet. With these services users can gather information, place and read electronic messages from other users, and download available files.

Electronic Mail

More often called E-Mail. E-mail is a fast, easy, and inexpensive way to communicate with individuals or groups on networked computers and computers equipped for Internet access. Besides basic correspondence, with some systems you can attach and send documents and other files.

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List of frequently asked questions and their answers.

Facsimile Machine (fax)

A telecopying device that electronically transmits written or graphic material over telephone lines to produce "hard copy" at a remote location.


Standards-based display format for communicating between videoconference systems from different vendors.

Fiber Optic Cable

Bundled glass rods (fibers) that are extremely thin and flexible and are capable of transmitting voice, video, and data signals in either analog or digital formats. This is accomplished with very little loss in signal quality. A single glass fiber can carry the equivalent of 100 channels of television or 100,000 telephone calls, with even more capacity possible by encasing many fibers within a cable.


The area of the earth's surface where a particular satellite's signal can be received. A footprint can cover one-third of the globe, but is usually less.

Frame rate

Frequency with which video frames are displayed on a monitor, typically described in frames-per-second (fps). Higher frame rates improve the appearance of video motion. Broadcast TV (full-motion video) is 30 frames-per-second.

Full-Motion Video

Equivalent to broadcast television video with a frame rate of 30 fps. Images are sent in real time and motion is continuous. Unlike compressed video signals (which tend to be blurry), full-motion video refers to high-quality signals, similar to what is received over a television set.

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Geostationary Orbit

An earth orbit located directly above the equator, approximately 22,300 miles above the surface. Satellites in this orbit rotate at the same relative speed as the earth itself. This allows earth antennas to remain fixed.


A menu-based system for exploring the Internet. Users locate resources by selecting resources from menus.

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H.320 Standard

A widely-used video compression standard that allows a wide variety of videoconferencing systems to communicate. H.320 includes a number of individual recommendations for coding, framing, signaling, and establishing connections.

Hard Drive (Hard Disk)

A rigid non-removable disk in a computer and the drive that houses it. Hard disks store more data and can be accessed quicker than floppy disks.

High Definition TV (HDTV)

Regular NTSC signals have 525 lines of resolution. HDTV has 1125 lines of resolution having over five times the video information than that of a conventional NTSC-type TV set. In spite of its obvious advantages, transmission requires extraordinary bandwidth of five times the capacity of a conventional TV signal. TV receivers are estimated to be 30% more expensive than today's most costly sets.


Text with links to other text. Documents written as hypertext contain text that when "clicked on" by the user with a mouse, links to other documents.

HyperText Markup Language (HTML)

Set of programming commands inserted around blocks of text that describe how to display it. HTML commands also display other media (graphics, sound, and video). Documents on the Web are often written in HTML.

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Instructional Multimedia

A form of computer-based training that incorporates a mix of media as the stimulus to the student. Possible media elements include sound, animation, graphics, video, text; whatever it takes to get the instructional message across to the target audience. See Multimedia

Instructional Systems Development

Systematic approach to the planning and development of a product to meet instructional needs and goals. All components of the system are considered in relation to each other in an orderly but flexible sequence of processes. The resulting instructional product is tried out and improved before widespread use is encouraged.

Instructional Television Fixed Services (ITFS)

A band of low-power microwave frequencies set aside by the Federal Communications Commission (FCC) exclusively for the transmission of educational programming, and licensed to public institutions. ITFS is typically used in urban areas and requires a specialized antenna. Receiving sites require a converter capable of changing signals to those used by a standard television set.

Interactive Video

Combination of a videodisc (usually laserdisc) or videotape and computer system that permits user response and participation, allowing for direct exchanges between user and software or among people. This instructional medium has limited use today.

Integrated Services Digital Network (ISDN)

Digital network with higher speed than found on the traditional telephone network. Even though ISDN uses existing phone lines, it does require specialized equipment. Because the network is all digital it can easily send voice, data, and video over the same line simultaneously.


A worldwide network of computer networks. It is an interconnection of large and small networks around the globe. The Internet began in 1962 as a resilient computer network for the U.S. military and over time has grown into a global communication tool of more than 12,000 computer networks that share a common addressing scheme.

Internet Courses

Students participate in the class by using the Internet for all or part of the coursework. The instructor posts a Web page which contains all relevant course information and assignments. Communication between students and instructors occurs by e-mail.


Inter-connected network within one organization that uses Web technologies for the sharing of information internally, not world wide. Such information might include organization policies and procedures, announcements, or information about new products.

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Programming language developed by Sun Microsystems that creates code for interactive applications that is executable on web pages by web browsers. These Java applications can execute on any platform--Mac, PC, etc.

JPEG (Joint Picture Expert Group)

Standard for the compression of still pictures, such as those that might be used on a Web site.

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Most popular type of satellite transmission for uplinking and downlinking. Ku-band operates on a higher frequency than C-band transmissions and requires smaller antennas.

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LAN (Local Area Network)

Communications network connecting computers by wire, cable, or fiber optics link. Usually serves parts of an organization located close to one another, generally in the same building or within 2 miles of one another. Allows users to share software, hardware and data.

Linear Video Editing

Editing analog videotape. Before digital editing or nonlinear video editing, video sequences were edited by inserting new frames and reconstructing the balance of the tape by adding the remainder of the frames. See Non-Linear Video Editing


A graphic, line of text, or both on a Web page that connects to another page on the same Web site or to one on a Web server located anywhere in the world. Links are "clicked on" to go to the Web page they specify.


Mailing list program for communicating with other people who have subscribed to the same list. Using E-mail, you can participate in listservs pertaining to your topics of interest. When you submit a message to the server your message is relayed to all those on the listserv. You receive messages from other participants via E-mail. It is similar to computer conferencing, but a listserv is asynchronous.

Logging On

Connecting to a computer network, typically through the use of a personalized identification code.

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Mainframe Computer

A large relatively complex computer. Its capacity far exceeds that of the microcomputer.


A computer with a microprocessor chip-based processing unit. Microcomputers are the original personal computers that many people use at home and at work.


High-frequency radio waves used for point-to-point and omnidirectional communication of audio, data, and video signals. Microwave frequencies require direct line of sight to operate. Obstructions in the path usually distort or block the signal. Growth of fiber optic networks have tended to curtail the growth and use of microwave relays.


Equipment that converts digital signals into analog signals for purpose of transmission over a telephone line. Signal is then converted back to digital form so that it can be processed by a receiving computer. Modems are typically used to link computers via telephone lines. Short for modulator-demodulator. Typical modems for home use are 14.4 kbps. 14 kilobytes per second translates into a transmission or receiving rate of approximately 1600 bytes per second.


Moving Picture Experts Group. The standard for compression and storage of motion video, for example, videos available though the World Wide Web.


Systems that support the interactive use of text, audio, still images, video, and graphics. Each of these elements must be converted in some way from analog form to digital form before they can be used in a computer application. Thus, the distinction of multimedia is the convergence of previously diverse systems.


The act of combining input signals from many sources onto a single communications path, or the use of a single path for transmitting signals from several sources. Advantages of multiplexing is that it doubles the capacity of television transmission and allows for simultaneous feed of independent programs for two audiences.

Multi-Point videoconference

A video conference with 3 or more sites. Sites must connect via a video bridge.

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National Television Systems Committee. The American engineering standard for horizontal video resolution lines, 525.


A configuration of two or more computers linked to share information and resources.

News Group

Discussion group on the Internet. Similar to electronic bulletin boards. Users are presented with a summary of discussion topics and can select from an organized menu and sub-menu structure.


An origination or reception site.

Non-Linear Video Editing

Editing video in the computer. Digital nonlinear systems provide high-quality post-production editing on a desktop computer. See Linear Video Editing

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One-Way Video/Two-Way Audio

An interactive conference, class, or meeting in which participants see and hear the speaker(s) at the originating site as well as hear participants at other receiving sites. Two-way audioconferencing is used for the real-time verbal interaction.

Originating Site

The site initiating the conference or meeting that is to be distributed simultaneously with technology such as audioconferencing or videoconferencing.

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P2 Chip Technology

Digital video storage media format featuring tapeless (non-linear) recording on a solid state flash memory card. P2 is short for Professional Plug-In.

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Rain Outage

Loss of signal at Ku-band satellite frequencies due to absorption and increased sky noise caused by rainfall or ice crystals in the upper atmosphere.

Real Time

An application in which information is received and immediately responded to without any time delay. See Synchronous

Receiving Sites

All sites, other than the originating site, participating in a course or meeting that is distributed with technology such as audioconferencing or videoconferencing.


The clarity of the image on video display screen. Three factors influence resolution: lines of resolution (vertical and horizontal), raster scan rate (number of times per second the image on a video screen can be refreshed or "lit up" again), and bandwidth.

RGB Monitor

Video display screen with colors Red, Green, Blue as light waves. The three colors combined in different ways produce all other colors.

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An earth-orbiting device used for receiving and transmitting signals. Each satellite has a number of transponders which receive the signal and bounce it back to earth, where it is received by any of the dish-shaped earth stations, then transmitted via cable, phone lines, or microwave to its final receiver TV set.

Search Engines

Permits searching of documents and databases accessible on the Internet. Search engines can be set up to search only content within one Web site or to search the entire Internet. Many search engine developers have their own web sites such as Lycos and Alta Vista. In addition to search engines there are index sites such as Yahoo, where links to Web sites are organized into categories so that you can browse categories rather than guessing at search terms.


Computer software developed for the public domain, which can be used or copied without infringing copyright. Programmers typically get paid a small one time fee from users who find the software useful.

Simplex Video

One-way video communication capable of origination and reception, though not simultaneously.

Solar Outage

Solar outages occur when an antenna is looking at a satellite, and the sun passes behind or near the satellite and within the field of view of the antenna. The field of view is usually wider than the beamwidth. Solar outages can be exactly predicted as to the timing of each site.

Switched Network

A type of system in which each user has a unique address (such as a phone number) that allows the network to connect any two points directly.


A type of two-way communication that occurs with virtually no time delay, allowing participants to respond in real time. Also, a system in which regularly occurring events in timed intervals are kept in step using some form of electronic clocking mechanism. See Asynchronous

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The process of transmitting or receiving information over a distance by any electrical or electromagnetic medium. Information may take the form of voice, video, or data.


Simultaneous conference to multiple sites distributed via audio (phone or other audio). Satellite videoconferences and videoconferences using compressed video are sometimes referred to as "teleconferences." To distinguish more accurately between these frequently used terms, using the term which uniquely describes the communication is preferred.


Use of telecommunications technology for medical diagnosis and patient care when the provider and client are separated by distance. Telemedicine includes pathology, radiology, and patient consultation from the distance.

Touch Screen

Input device over the television or a special computer screen that is used to simplify user input and response. The user touches the screen rather than a keyboard, keypad, or mouse to control the output. Touch screens work best with menus or multiple-choice decision points, and also allow some simulation of hands-on training, i.e. pointing to parts of a body.


The electronic equipment on a satellite that receives signals from an uplink, converts signals to a new frequency, amplifies the signal, and sends it back to earth. Satellites are usually equipped with 12 to 14 transponders.

Two-Way Video/Two-Way Audio

Interactive video in which all sites are in visual contact with one another. Some form of audioconferencing is used for real-time verbal interaction.

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Programs are "uplinked" to the satellite transponder and "downlinked" to the ground receiving dish.


The transfer of copies of a file from the user's own computer to a remote database or other computer. The reverse of downloading.

URLs (Uniform Resource Locators)

The address system used by the Internet to locate resources such as websites. A URL includes the type of resource being accessed such as gopher or hypertext, the address of the server, and the location of the file. For example, the complete URL for the ALPHTN website is "Http://" indicates the access method as Hyper Text Transfer Protocol. "" is the address of the server. "/ALPHTN/" specifies the directory the file is located. "Index.asp" is the initial page of the ALPHTN website. Web browsers will assume "http://" and "index.aspl."


US Distance Learning Association.

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A meeting, instructional session, or conversation between people at different locations relying on video technology as the primary communication link. Communication is 2-way audio with either 1-way or 2-way video. The term, videoconference, is sometimes used to refer to conferences via compressed video, conferences via land lines, and broadcasts via satellite. To avoid confusion, using the term or phrase which uniquely describes the communication technology is recommended.

Video Bridge

Specialized equipment that permits three locations or more to be joined together in a videoconference.

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Web-Based Training (WBT)

A form of computer-based training in which the training material resides on web pages accessible through the World Wide Web. Typical media elements used are text and graphics. Other media such as animation, audio, and video can be used, but require more bandwidth and in some cases additional software. The terms "on-line courses" and "web-based instruction" are sometimes used interchangeably with WBT.


Communicating to multiple computers at the same time over Internet by "streaming" live audio and/or live video. Through compression and decompression of the signal, audio and video are experienced in real time over Internet. Examples of commercial products emerging in this area include RealAudio, VDOLive, and VXtreme.


Related collection of web documents. The address for a web site (see URL) takes you to the initial page, or home page. From the home page you can go to all the other pages on the web site.

World Wide Web (WWW)

A hypertext-based, distributed information system originally created by researchers at CERN, the European Laboratory for Particle Physics, to facilitate sharing research information. The Web presents the user with documents, called web pages, full of links to other documents or information systems. Selecting one of these links, the user can access more information about a particular topic. Web pages include text as well as multimedia (images, video, animation, sound). Servers are connected to the Internet to allow users to traverse (or "surf") the Web using a Web browser. In addition, many other resource formats such as Gopher are accessible by Web browsers.

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Source: CDC Glossary of Selected Distance Learning Terms and Phrases

Page last updated: May 13, 2021