What is Secret Slut?
1.
someone who engages in a long term secret affair with a neighbor, friend, or acquaintance.
Did you hear he is a giant secret slut? They were bumpin' uglies for 10 months before we found out!
See
2.
some of low character; some one lacking virtue and honor. It should be noted that this person is not suspected of these crimes of chastity
A: You will never believe what I just found out!
B: ?
A: You remember Susie, that real quiet girl? Apparently she's been hookin' since she was old enough to drive.
B: I never would've suspected her of being a secret slut! She seemed like such a nice girl
See