A mat is a type of item introduced in Generation III, debuting in Pokémon Ruby, Sapphire, and Emerald. In those games, mats can be used to decorate the player's secret base. They seem to be the Generation III equivalents of carpets from Generation II.
These eleven mats have special effects when the player steps on them:
The note mats are available at the Slateport City marketplace, and the other three are available at the Lilycove Department Store.
These seven mats each have a design based on a move and can hold up to five dolls or cushions:
These are available at the Lilycove Department Store.
In Generation V, mats make a return. However, they can be used to customize the Pokémon Dream World, and can be bought from Berries.