A term used to describe a version of the female species who is in no conceivable way willing to interact in sexual activity. No matter how hard you try, she will not give it up.
1.) "Dude! I'm totally gonna hook up with that Tammy chick tonight!"
"No way man, she's a virgin Mormon. There is no way you're getting past that force field. That's mission: impussable."
2.) "Man, i totally thought i was going to score with this drunk chick last night, but she would not put out. She was being so impussable."