What is "missingno."

, or MissingNO, is an unofficial Pokémon species found in the video games Pokémon Red and Blue. Standing for "Missing Number", MissingNo. are used as error handlers by game developer Game Freak; they appear when the game attempts to access data for a nonexistent Pokémon species. Due to the programming of three in-game events, players can encounter MissingNo. via a glitch. The species was first documented by Nintendo in the May 1999 issue of Nintendo Power.

Encountering MissingNo. causes graphical errors and the mass replication of the sixth item in the player's item menu; the latter effect resulted in the glitch's coverage by strategy guides and game magazines. IGN has noted MissingNo.'s appearance in Pokémon Red and Blue as one of the most famous video game glitches. Fans of the series have attempted to rationalize MissingNo. as part of the games' canon, and sociologists have studied its impact on players.