As in a Fat Person and/or an extremely large buttocks. Can also be used in an insult, calling someone "fat" may not always work, so adding "Fatass" My help to boost your insult to astronomicalheights
A fat bitch. So fat they cant even see their penis anymore. Someone who the opposite sex is ASHAMED to be seen with. A large corpulent person with sausage fingers and a fat mush face.