Software defect (nonfiction)

A page from the Harvard Mark II electromechanical computer's log, featuring a dead moth that was removed from the device.

A software defect (or bug) is an error, flaw, failure, or fault in a computer program or system that causes it to produce an incorrect or unexpected result, or to behave in unintended ways.

A program that contains a large number of defects, and/or defects that seriously interfere with its functionality, is said to be buggy.