A Fighting Game term which refers to the box-like or circle-like descriptors attached to a character's model showing where they can and cannot be hit. When the hitbox of an attack meets a character's hurtbox, the result is a successful hit. Hurtboxes are typically invisible during normal gameplay and do not line up exactly with a character's model.
In Super Smash Bros. Melee, Mr. Game & Watch's shield doesn't cover his entire hurtbox, meaning he can gethit even while shielding.