A superhero for whom there's more than one person in their head. Bruce Banner and the Hulk are a plural system, and so are Steven Grant, Marc Spector, and Jake Lockley. Although Banner and Hulk have integrated into a single personality by the time of Endgame. In She Hulk, Bruce is actually really surprised that Jen isn't plural. I guess in the MCU he hasn't realised that his plurality is caused by being beaten by his father like in the comics. He thinks his plurality is caused by gamma radiation up until Jen turns into a hulk but isn't plural.