Definition Audio-visual is, of course, a combination of two words: audio referring to that which we can hear, and visual referring to that which we can see. The basic frame of reference here limits our application of the term to a speaker and his audience, although they are not necessarily in the physical presence of one another, as in the case of a motion picture or television presentation. The term "aids," used in reference to the speaker, rules out his physical presence (visual) and unrecorded voice (audio). These are the essential elements which make him a speaker, and therefore cannot aid him (his voice cannot aid his voice). Audio-Visual Aids The term "audio-visual aids" is commonly misapplied. The aids themselves must be something either audible or visual, or both. The common types of audible aids are the spoken word, recognizable sound effects, and music. The most frequently used visual aids are people, pictures, cartoons, graphics, maps, the printed word, and three-dimensional models. When we talk about a motion picture projector or a blackboard, we are talking about the means of presenting the aids, and not the aids themselves. Audio-visual materials can be divided into those which present the aids in their original form, and those which reproduce the original form. In the following paragraphs, we will briefly define the most common means of display which make sights and sounds useable in the speaker-audience situation outlined above. They will be discussed in further detail in later chapters. Visual Aid Display Equipment 1. Animation. Movement may be given to different types of visual aids. The materials necessary to do so fall in this section, but since they are usually improvised they cannot be specifically defined. Examples are given later in this report. 2. Blackboard. Black, green or other colored slate or composition board, or a specially painted surface which will "take" erasable white or colored chalk. 3. Bulletin Board. Flat board of cork, composition or other wood or material to which visual aids may be attached with pins, tacks or staples. 4. Easel or A-frame. Any type of frame which will hold flat-surfaced visual aids of any given size; characterized by the artist's easel, which is similar in structure to the letter "A," with a third leg used as a brace.