noclip

The story

From no clip, possibly chosen originally as a debug code to allow developers to investigate clipping (in the sense of a computer graphics technique to not render unseen objects) or due to a mix up between clipping (in the sense of checking the player remains inside the boundaries of the play area) and collision detection. Perhaps originates from the 1991 game Commander Keen IV: Secret of the Oracle, where using the appropriate cheat code displays a message "No clipping ON".