(1) A woman who is wearing an outfit which you wish you had the courage to wear.
(2) A woman who you would like to sleep with, who is sleeping with people other than you.
(3) A woman who is sleeping with a person you want to sleep with.
Guy: Did you see how short that girl's skirt was? What a slut.
Girl: Yeah, it's obvious that because she chose to wear a skirt we have an opinion about, she is sexually promiscuous.
Guy: I only date virgins. Women who make adult decisions to sleep with men other than me are all sluts.
Girl 1: I can't believe she slept with him. What a slut.
Girl 2: Yeah, and implying that she sleeps with lots of people totally makes us better than her.