Backdoor Key

n. The act of opening one's backdoor, that is, anal sex

"Hey, you know I wanna be your backdoor key, its about time I opened it up"

John: "Did you hear about Matt?"
Chris: "No what happened?"
John: "While he was fucking Shirley she gave him the key to her backdoor"

by Mitch Tight and Bright March 22, 2011

Key to the backdoor

It's a slang for the term anal. Meaning you put the male genitalia into the female's rectum.

E.G for key to the backdoor:

Male : I'll give you the key to the back-door baby!
Female : I'm not that dirty thank you... I don't like anal.

by Husky123654 December 16, 2014