What type of undocumented yet benign hidden feature launches after a special set of commands, key combinations, or mouse clicks?

Easter egg

Explanation:

An Easter egg refers to a secret message or a feature hidden in an application. It is often used to display development team names, or to show a funny message. In order to view an Easter egg a special sequence of keystrokes or special commands are used to display it. Easter eggs in games are also common and may result in humorous scenes, or a hidden level that gamers can find while playing. Easter egg refers a secret, unknown yet innocuous feature that releases by entering a set of special commands. Programmers usually insert Easter eggs during software program development for notoriety or fun.