code|character code]] which prodces a standard audibile warning from the computer or terminal. In the teletype days it really was a bell, since the advent of the VDU it is more likely to be a sound sample (e.g. the sound of a bell) played through a loudspeaker.
Also called "G-bell", because it is typed as Control-G.
The term "beep" is preferred among some microcomputer hobbyists.