From Bulbapedia, the community-driven Pokémon encyclopedia.

Pikachu is a species of Pokémon. It may also refer to specific Pokémon of that species:

• A Pokémon belonging to Ash Ketchum: Ash's Pikachu
• A Pokémon which belonged to Lt. Surge before evolving: Lt. Surge's Pikachu
• Ash Ketchum himself after his transformation in Hocus Pokémon: Ashachu
• A Pokémon belonging to Victor: Puka
• A Pokémon belonging to Ritchie: Sparky
• A character in Pokémon PiPiPi Adventure: Pikachu (PiPiPi)
• A Pokémon belonging to Isamu Akai: Pikachu (Pocket Monsters)
• A Pokémon belonging to Red in Pokémon Special: Pika
• A Pokémon belonging to Yellow in Pokémon Special: Chu Chu
• The sole starter Pokémon in Pokémon Yellow: Red's Pikachu (game)

It can also refer to:

• One of the Generation I games known as Pocket Monsters Pikachu in Japan: Pokémon Special Pikachu Edition
• A small handheld, the Pokémon Pikachu
• A game that stars a Pikachu, Hey You, Pikachu!