Hit dice are statistics in the form of dice that describe the overall strength of a character or creature, most often being used to calculate a character's hit points. In its most common usage, a player rolls all of a character's hit dice to determine their maximum hit points.
Hit dice were introduced to role-playing games in early Dungeons & Dragons, based on concepts from wargaming. In wargaming, hit dice represented a unit, including its size, strength and ability to hit for damage. Once adapted for role-playing games, the type of die used for a character, and the progression in ability to hit, was determined by character type (specifically class in D&D) or creature type.