A dewlap is the flap of fat and skin that hangs down under the jaws of many vertebrates. The term can also refer to other structures in the same area of the body like the vocal sac of a frog.
Dewlaps serve varying purposes for different animals. Lizards can inflate and deflate their dewlaps to communicate with other lizards. Female rabbits develop dewlaps when they are ready to reproduce. They often pull fur from their dewlaps to line their nests for their young. Moose use the dewlap to scent-mark females and that the size of a moose’s dewlap may indicate its dominance level.