From Bulbapedia, the community-driven Pokémon encyclopedia.
Side series Pokémon games are games developed by Game Freak that are not part of the main series. They are usually released for Nintendo's home consoles instead of handheld consoles. Sometimes, it is possible to connect the main series games to certain side series games in order to get a reward, normally a special Pokémon.
The Stadium series consists of games focusing on the same style of Pokémon battles seen in the main series, but with no role-playing elements whatsoever.
The Box series consists of games in which players can store Pokémon from their copies of main series games.
The Coloseeum series consists of games with a strong role-playing element similar to main series games, but without core elements such as collecting Badges to compete in the Pokémon League.