The Pokédex in the Pokémon videogames includes information about every Pokémon in that version of the game. Each Pokédex entry typically includes the Pokémon's name, description, image, location and type, in addition to its height and weight.
The Pokédex is given to players at the beginning of each game by a professor. One of the main goals of the game is to fill the Pokédex by catching every Pokémon available in the game.
Versions of the Pokédex have been included in every Pokémon game to date, with minor changes between generations. In the first generation, the Pokédex gives a Pokémon's number, name, category, height and weight, in addition to its cry, area and a short description of the Pokémon. In later versions of the game, the entries were expanded to include, among other things, a footprint, differences between forms of the Pokémon, and a display showing the Pokémon's height relative to the trainer.
Pokémon do not appear in the Pokédex until a player has met them either in battle against another trainer or in the wild. A more detailed description of a Pokémon appears once the trainer has obtained the Pokémon by catching it or trading for it.
A National Pokédex, or one that includes every Pokémon in the entire series, is typically given to the player later in the game, usually after defeating the Elite Four.