Overview
A Pokémon trainer (ポケモントレーナー, Pokemon torēnā), in the broadest sense, is "a person who handles Pokémon in a ball".
Players in the Pokémon games become Pokémon Trainers, and one of their goals is to become a Pokémon League Champion by raising Pokémon, repeatedly fighting Pokémon battles, and traveling around the country while collecting gym badges scattered throughout the regions.
But not only those who aim to become champions are Pokémon trainers. Even if you do not aim to become a champion, you are called a Pokémon Trainer if you have a Pokémon in a ball.
In fact, there are trainers of all ages, races, and professions everywhere in the game.
External Links
English
Pokémon Trainer - Bulbapedia, the community-driven Pokémon encyclopedia