Thunderbolt is a move used by Mallow in the game Super Mario RPG: Legend of the Seven Stars. It is a Thunder-based move that requires only 2 FP to use. Mallow already knows this move without having to level up.
With Thunderbolt, Mallow can attack every enemy on the screen for electrical damage. This is useful when dealing with a group of enemies (especially those with a weakness to Thunder such as the Shysters). However, the move itself is a tad weak. A stronger version of Thunderbolt is called Shocker but it only strikes a single enemy for high damage.