An acronym that stands for "Big Ole Titties And a Fat Ass".
Thought to have been invented by bored Submarine Sailors in the U.S. Navy during a random bullshit session.
Used whenever a desirable female is witnessed as a way to discreetly (or indiscreetly) compliment how great of a body she has, and due to it being a lesser known acronym, is usually appropriate to yell or speak in her direction so your buddies will agree and a chorus of "BOTAFA!" will arise.
A really hot girl walks out of a store across the street.
Guy: "Damn, now THAT is BOTAFA!!"
Other guys: "BOOOOTAAAFFAAAA!!!"
Girl: "What's that mean?"