A word used to describe a female's, commonly of the african american persuasion, ass. It is used to describe characteristics of the ass, mainly the size (large) and the look (a bit nasty, big and jiggly.)
Billy: See that chick Kelsey over there? She's got a badonka donk butt!
Tommy: Nah, that girls a babe! She's got a nice, cute butt! She's actually just cute all around!
Billy: Oh, you are right. Tommy, you are the coolest kid in the world.
Billy: I love you.