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1.
Aussie expression for a girl that is not necessarily pretty, but you would root her because she has a slutty attraction about her.
“Oh Brandy, I’d like to root her, only because she’s got the slut factor”
by Robby101 November 01, 2006
 
2.
A slut-factor is a scale for quantifying the sluttishness of a girl from 0 to 10, with 10 being the 'ultimate slut' with no ethics. A girl with a slut-factor of 0 is a very nice girl.

Different individuals or organizations can create different computation methods to calculate slut-factor.
Girl-1 : Girl-2 has slept with almost all the freshman guys; she has a perfect 10/10 slut-factor.
by cade_skywalker June 07, 2011