The Pokédex is an essential tool for Trainers in the Pokémon universe. It provides data on all Pokémon contained within its database, though the method of acquiring and presenting this information varies across different media. Only a select few Trainers receive a Pokédex at any given time, usually those deemed to have extraordinary potential and skill. Regional Pokédexes offer details about Pokémon native to specific areas, whereas the National Pokédex catalogues information on every known Pokémon. Though the idea of a Pokédex has been around for a long while, its digital form is a more recent innovation credited to Professor Oak.
Pokédex entries typically describe each Pokémon in just two or three sentences. These entries might include background on the Pokémon's natural habitat, behavior in the wild, historical context, or anatomical features. Additional details provided by Pokédex entries encompass height, weight, vocalization (cry), footprint (prior to Generation VI), location, alternate forms, and a visual depiction of the Pokémon.
(Source: Bulbapedia)
