A 'butterface hottie' is a woman who has an excellent BODY (tits, ass, legs whatever it may be) but a 'suspect' face (you take away the body and she would likely not be attractive). However, the face cannot be such a negative that it takes away from the attractiveness.

So a girl with a not-so-pretty face but great body (butterface hottie) is different from a girl who is downright unattractive facially (ugly) even with a great body (butterface)

Many women take offense to being labelled a butterface hottie/butterface but being a 'butterface hottie' means you're still hella sexy and the truth of the matter is simply this - You can't all be pretty but you can still be scorching hot and cause erections everywhere you go