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2.
An inch long crevice found on the derriere, that has escaped the modest covering from trousers.
"Cor, look at her bumcrack, the dirty slapper! You could park a car in that!"
by BumcrackTheDog November 02, 2004
 
1.
To un-intentionally show you bum. Usually only the top part is revealed when bending down. Or if you’re a builder of some description you will already be wearing loosely fitting pants that assist in revealing your bum crack.
I was walking along the street when I saw two moons looking at me. The fattest builder was showing every one his bum crack. To which I shouted out say no to crack!
by Harpo July 20, 2004
 
3.
Completely pointless person, thing or action. Something that offers no value for its existence.
Your goatee is a bumcrack.

That bumcrack professor barely teaches us anything in class.
by Food fiends December 05, 2010