Computer Icons are a phenomenon of software in the late Twentieth Century. Basically, they consist of small, symbolic pictures which appear on your computer screen and are supposed to help you fathom out what that particular program, function, or button does. They also look incredibly friendly and welcoming when compared to a blank screen and a command prompt, and it was this which led the genius programmers at Xerox to develop the first commercial interface using icons in the early 1980's. (Apple like to claim that they invented the Icon, but this is patently untrue and typical of the sort of one-upmanship that goes on all the time in IT).
The concept behind Icons is that you can indicate what a particular feature of a program does by using an example from the 'real world' (i.e. A Folder to keep files in, a Notepad to keep notes in, get the idea?) 1 Having almost singlehandedly invented the modern computer interface, Xerox then dumped it in favour of something less successful. (History does not record what).
Microsoft, however, adopted the idea for Windows, and of course, suddenly everyone had to have them. This has led in recent years to the poor icon being stretched incredibly thin in the search for yet more and more obscure symbols to indicate computer functions that have absolutely NO real life equivalent (i.e. just about anything on the Internet) Nonetheless, it appears the humble icon is here to stay.