Pokédex
A Pokédex is an invaluable tool to a trainer in the Pokémon world. It gives information about (almost) all Pokémon in the world that are contained in its database. In the games, it lists the number of Pokémon seen and caught. In the anime, simply pointing it at a target Pokémon will give someone the Pokédex entry for that Pokémon. Pokédexes in both the games and anime are not given to all trainers, but given to trainers of exceptional potential and skill. In both the games and the anime, Ash and Gary both got Pokédexes from Prof. Oak, although via different circumstances. Ash was notorious for using his Pokédex in situations where he had no idea what was going on, and was just as notorious for always being behind Gary in Pokédex entries.
Pokédex entries are typically only two- or three-sentence bits of information about the Pokémon referred to. In some events it gives background information on the habitat or activities of this Pokémon in the wild; at other times it gives other bits of information on the Pokémon's history or anatomy. A typical entry would be one of Bulbasaur, which states:
"A strange seed was planted on its back at birth. The plant sprouts and grows with this Pokémon. "