Question

I see it in the pokedex.I'm wondering.

Answer 1

The pokeathlon is a competition involving Pokémon racing and similar athletic competitions, in the manner of Olympic track and field competitions. It was introduced in Pokémon HeartGold and SoulSilver. The Pokéathlon Dome, where the competitions are held, is north of Goldenrod City, next to National Park.

Answer 2

It's a place where your Pokemon can compete to get athlete points. Athlete points are used to buy items in their shop. It's basically just a mini game. You can enter it around the bug catching park.