A chick who gets what she wants, which is usually sex. She's usually only called a "slut" by guys who wish they could get away with having the kind of power she has over the opposite sex.
"Have you heard about what's-her-face? She's a slut
"Yeah, she gets more ass than a toilet seat! What's her secret?"
"I'm afraid it's out of our grasp...we're just a couple of no-pussy-getting-motherfuckers!"