A girl who one might generally call a butterface but who possesses an ass worthy of attention such that it compensates for and exceeds other possible faults. Butterass negates slight to medium cases of butterface.
Him: "Damn, man, she's a bitugly..."
Me (Pointing at her posterior): "Maybe...butterass"
Him: "Oh damn!"
comes from the words butter, cash, and money, all combined to make one super adjective used to describe something incredibly 1337, pwnerific, or just damn cool