A glitch is a short-lived fault in a system. The term is particularly common in the computing and electronics industries, as well as among players of video games, although it is applied to all types of systems including human organizations.
In electronics, a glitch is an electrical pulse of short duration that is usually the result of a fault or design error, particularly in a digital circuit. For example, many electronic components such as flip-flops are triggered by a pulse that must not be shorter than a specified minimum duration, otherwise the component may malfunction. A pulse shorter than the specified minimum is called a glitch. A related concept is the runt pulse, a pulse whose amplitude is smaller than the minimum level specified for correct operation, and a spike, a short pulse similar to glitch but often caused by ringing or crosstalk.
In video games, a glitch is a term used by players to indicate a bug or programming error of some sort. It may refer to either a helpful or harmful error, but never an intended behavior. For example, a programming error that makes the game freeze is often referred to as a glitch, and so is an error that gives you 100 lives automatically. However, some glitches' occurrence has been discovered and described by doing certain tasks in a certain order. For example, the Missingno and Glitch City glitches in the Pokémon series follow this principle.
The practise of exploiting glitches in video games is known as "glitching". For example, in an online game someone may use an error in the map to get an advantage. This is sometimes considered cheating, but sometimes just considered part of the game.