Sinnoh is the region represented by Pokémon’s fourth-generation games.
The fourth generation began with Pokémon Diamond and Pearl for the Nintendo DS in Japan in 2006. The games introduced a new set of Pokémon, a dual-screen interface, online trading and battling features, and the Sinnoh region as the main setting.
Sinnoh is based largely on Hokkaido, Japan’s northern island. Its geography includes snowy mountains, forests, lakes, and coastal areas, giving the region a colder visual identity than many earlier settings. Pokémon Platinum later expanded the same generation with additional story content.
Sinnoh is sometimes confused with Hisui. Hisui is the ancient name for the same broad land area in Pokémon Legends: Arceus, but Sinnoh is the standard name used for the fourth-generation setting. Johto, Hoenn, and Kalos belong to different generations.