1. demo /de'moh/ 1. A demonstration of a product, often of an early version or prototype. A demo is a far more effective way of inducing bugs to manifest themselves than any number of test runs, especially when important people are watching. 2. demo version. 3. A program written to demonstrate the programmer's coding ability and/or the power of the computer it runs on. Such demos are nearly always written in machine code and traditionally feature scrolling text about the author, his friends, his code and anything else he fancies and animated graphics. [Jargon File] 2. a visual presentation showing how something works; "the lecture was accompanied by dramatic demonstrations"; "the lecturer shot off a pistol as a demonstration of the startle response"