1) A person who is very large in circumference, or has a higher than average % of body fat. See fat ass tub of lard obese
. The term generaly used in IM conversations and is spelled with an H to give importance to the a, and makes the reader pernounce it differently.
Person 1: eeewww, look at that Rosie O'donnel
Person 2: Yeah, she's a real fahtass