Glitch City (Japanese: 故障都市 Wrecked City) is a term used by players of the Pokémon games to refer to corrupted maps that result from a glitch present in the Generation I games of Pokémon Red, Blue, and Yellow. Glitch Cities in Pokémon Yellow are different from those in Pokémon Red and Blue.
http://bulbapedia.bulbagarden.net/wiki/Glitch_City