A girl who is not hot in any way but still tries to dance like a whore at clubs; a wannabe slut; also very clingy girl, with same characteristics
Derived from the aspect that real sluts are "loose", while a leesey is not loose, but wants to be, so she is "leese".
Guy: Dude, where have you been?
Wingman: You SO owe me man, I got stuck with another leesey!
Guy: *panting* Man, we gotta go!
Other Guy: What is it?
Guy: *looks over shoulder* That leesey just tried to kiss me!
Other Guy: *panicked* Oh (expletive), duck down and follow me!