Easter egg (software)
An easter egg is a hidden bit of software which (like a real Easter egg) can be discovered, generally by entering an undocumented command. Computer games and DVD movies sometimes have easter eggs.
Computer programmers may add an easter egg with or without the connivance of their employers.
The very first easter egg for a gaming system was the difficult to find (and entirely unauthorized) "Created by Warren Robinett" screen in the Atari 2600 game "Adventure."