Pikachu’s name in Japanese is “ピカチュウ” (Pikachuu). The direct translation of that name into English is “Spark Mouse”. 「ピカピカ」pika-pika is Japanese onomatopoeia for a peal of lightning, or for similar electric flashing. 「チュー，チュウ」chū/chuu is for the sound a small animal such as a mouse makes.

Pikachu (Japanese name: ピカチュウ Pikachuu). The most famous Pokémon of all. ピカ (pika) comes from the word ぴかぴか (pikapika), meaning 'shiny', and チュウ (chuu) is the onomatopeia for the cry of mice. So Pikachu means 'shiny mouse'.

“Pika” is from pikapika, which means to sparkle or glitter. “Chu” is from chuchu, the Japanese word for the sound mice make. So put them together, and you get “Pikachu,” AKA “Sparkle Mouse Noise.”