Definitely different from girls who happen to party hard and are willing to "sell" themselves for drugs or other items, the "party girl" is a girl who simply enjoys partying.
She may drink, but she doesn't get sloppy. She is a good friend, with an unspoken code existing between her and her girls, providing protection of one another and knowing when to step in and take her friend(s) home or stop them from doing something stupid. Sometimes associated with slut or whore because they also get along well with guys, otherwise known as a "guys girl", and many other women (and some guys who have been turned down by said "party girl") because they are jealous and need to be petty. A true party girl knows how to have a respectably good time and simply enjoys spending time with her friends, listening to good music and dancing in a circle with her friends. Oftentimes, a girl who doesn't stay home waiting for guys to call her on the weekend and rather goes out with her girls to a club or party, will be called a party girl in a derogatory sense.
Different from a girl misconstrued as a "party girl" who does drugs often, as that is an addict. Different from a girl who will sleep with random men for favors, as that is a whore and different from a girl who has low self-esteem and will sleep with anyone who gives her attention, as that is a slut.
Jen: Hey, Gina and I are heading out to the club Saturday night. There's supposed to be great music and a full dance floor. Wanna go?
Lina: Uh, yeah?!
Jen: What happened to John? You were going to see him Friday or Saturday night, right? This won't interfere, will it? I'll understand if you can't go, but we'd love to have you.
Lina: Well, it's already Thursday and I haven't heard from him. I was actually going to ask you what you were up to this weekend. Lol.
Jen: Ah, that's our girl! We're gonna have a great time! Laaaaaadies night! w00t!
Lina: Indeed! And we now have a full circle to block the guys with! Win! Let's give a ring to Elise and Maggie, too. They're always good party girls without drama, and they're not sluts, so we won't have to worry about keeping an eye on them if they drink. Fantastic.