The Pokédex category glitch is a glitch which only occurs in version 1.0 of Pokémon FireRed and LeafGreen, where only the first word in a Pokémon's category name is displayed. For example, Pidgey is called the "Tiny" Pokémon instead of the "Tiny Bird" Pokémon.
In Pokémon Ruby, Sapphire and Pokémon Emerald, the glitch does not occur, despite Ruby and Sapphire being earlier releases and featuring category names with more than one word.