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!
ayon kay Harpo ika-20 ng Hulyo, 2004
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!"
ayon kay BumcrackTheDog ika-02 ng Nobyembre, 2004