Hit Dice

Hit Dice (typically notated as HD), literally, are the number of and type of dice that a creature rolls for their hit points. Most often, they are referenced as a general case indicator of a creature's level. Every monster has a number of racial hit dice that are inherent to the creature, and any creature or player character with class levels has a hit die for each level of a class they have (creatures with racial and class hit dice add them together to get their total HD). In the case of player characters, there are few to no situations where they would have hit dice that do not come from their class, so their HD would equal the sum of their class levels, or total level.