The term computer-generated most often refers to a sound or visual that has been created in whole or in part with the aid of computer software. It can, but does not customarily, refer to something produced solely by computer hardware, like a noise from a hard disk drive or a printed page from a printer (although the object printed on the paper may be computer-generated, the physical page itself is not).
Sounds and visuals are the most easily computer-generated objects. They are created either from the ground up, or by using real-world models recorded by a microphone or camera, over which computer-generated objects are placed.