Bug

A "bug" normally refers to a programming error in software. The process of correcting bugs is called de-bugging. The word comes from computer errors from the first mainframes, which sometimes experienced errors due to actual, living insects, or "bugs", getting caught within the circuitry, which was large and exposed. Additional software complexity always increases the probability of additional bugs.

The term "glitch" is sometimes used interchangeably with "bug", but it is most often meant to refer to a hardware malfunction, rather than a programming error.