What species is Pikachu officially classified as in the Pokémon games?

Pikachu is officially classified as the Mouse Pokémon.

Pikachu is an Electric-type Pokémon introduced in the first-generation games. Its species classification appears in Pokédex descriptions and is separate from its elemental type: “Mouse” describes the fictional species category, while “Electric” describes its battle type.

Pikachu is National Pokédex number 025 and evolves from Pichu when friendship is high, then evolves into Raichu when exposed to a Thunder Stone. In the original games, Pichu had not yet been introduced, so Pikachu was encountered as a standalone early-generation species.

The anime made Pikachu the best-known Pokémon by giving Ash Ketchum a Pikachu as his partner. That popularity helped turn Pikachu into the franchise mascot, but it did not change the official species classification. “Electric mouse” is a useful informal description, while “Mouse Pokémon” is the canonical category used by the games and reference material.