A girl who is not only a slut, but a very dirty slut, and not in the good way. A slurt is someone you would not want to sleep with because of the high risk of contracting syphilis from her slurty cunt.
(Slut + Dirt = Slurt)
"Hey dude, don't you think Deborah's torn up jeans look hot?"
"Oh, you mean that pair she wears every day?"
"yeah, the ones with the grass stains on the knees from when she gave Chad a blow jay outside at the new years party!"
"She is such a fucking slurt!"