From Bulbapedia, the community-driven Pokémon encyclopedia.
A snow tile is a tile introduced in Pokémon Diamond and Pearl. The player can sink into the snow at four different levels: sinking only minimally, which does not affect movement speed; sinking a moderate amount, preventing running; sinking a lot, preventing running and halving walking speed; and sinking the farthest possible, preventing running and reducing walking speed to 1/4. It is not possible for the player to cycle over a snow tile. In Diamond, Pearl, and Platinum, snow tiles can be found on Route 216, Route 217, Acuity Lakefront, Snowpoint City, and Mt. Coronet. In HeartGold and SoulSilver, they appear at Mt. Silver and at the Sinjoh Ruins. In Pokémon X and Y, snow tiles are found on Route 17 but can only be navigated through while riding on a Mamoswine.
Certain moves have special effects when used in a battle on a snow tile.