Beep is the generic term for whatever sound a computer makes when it's trying to tell you something. If you press the wrong key or click on something you shouldn't, the computer will beep at you. Sometimes it beeps just to let you know that it has started or finished doing something (like copying a file). You can customize the beep sound in some computers. In particular, newer Macs and pcs with Windows 3.1 come with several sounds you can assign to various types of "events" in the system. Hundreds can be added, and you can even make your own sounds.
An informal name for the BELL character, ASCII code 7 or "G (CTRL+G),and a literal description of the feeble noise emitted through the tiny sound generator on its motherboard by an IBM PC that is not fitted with a sound card.