Although much has been written about techniques of artistic expression in the various media and about the social implications of the more persuasive of these, there is little information on communications theory which is useful to those who must make decisions concerning the applications of this new technology. Information refers to something which may exist in space or time while instruction refers to an entire process. Within this framework, communication media is defined and described and a set of criteria are proposed by means of which communication media may be distinguished from nonmedia, one medium distinguished from another, discrete media distinguished from multimedia applications, and instructional media distinguished from instructional aids. A two-dimensional classification system for communication media is proposed: in one dimension seven classes are defined, based on ways of representing information; in the other, communication media are divided into two groups, telemedia and recording media. Twenty-eight specific communication media are defined and described. Standard audiovisual terms and phrases have been used, and a glossary is provided. (MM)