Teach Pokémon to understand
The power that's inside

from Pokémon – Pokémon Theme Song Lyrics on Rap Genius

Meaning

A Pokédex is designed to catalog and provide information regarding the various species of Pokémon.

Whenever a Pokémon is first captured, its height, weight, species type, and a short description will be added to a player’s Pokédex. Each region has its own Pokédex, which differ in looks, as well as the species of Pokémon catalogued

A good video example of what a Pokédex does.
http://www.youtube.com/watch?v=j0FuYMCyEMU

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