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1.
When a girl has no ass
Paris Hilton has a long back, she needs to lay accross the toilet seat so she dont fall in.
by Joey from SD January 04, 2004
 
2.
1. A term used to describe women who lack a definable posterior.
1a. A girl/woman with noassatall syndrome.
1b. The opposite of bootilicious.
1c. Lacking in the booty department. A person devoid of a sufficient amount of jelly in the booty, giving the appearance of their back extending further than it really does. Hence, longback.
I've seen black girls, latin girls, and even white girls that got that booty. But asian girls? They're mostly longbacks.

Ray: "Damn...I need some ass tonight!...let's see...
Mike: "Hey what about that one over there? *points to some 45 yr old woman*
Ray: "Ew what? She's not even a MILF. You tryna sabotage me?? She's a longback for christ sake!"
by Anubikai March 15, 2006