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2.
A girl who is knida whore-like and easy to get in the sack.
"Man, that Ashley really is a fast girl" "Yeah man, I fucked that bitch up the wall the day I met Her!"
by ATown BTown April 10, 2006
 
1.
can be either someone whos a slut( or at least gives the idea that she's easy) and/or a really fast runner
( usually the best is a combination of both, but being more of a flirt than actually putting out)
"fast girls finish first" -nike running shirt
by xcrunner06 April 30, 2006
 
3.
A girl who has little ambition in life. One who parties heavily and lacks purpose, job or career goals.
I want to hit it with that fast girl.

No one wants to date a fast girl.
by MissVirginific September 06, 2010
 
4.
A woman who rides her R1.

A woman who is capable of introducing you to a whole world of hurt if you disprespect her.
Daaamn you see that Fastgirl? She rides the shit out of her R1!
by Fastgirl October 29, 2008