2. Refering to the butt of yourself or another (e.g. butt crack)
3. To show the spot where your back becomes your butt (e.g. plumber's crack)
4. To open (usually refering to your legs, primarily used in australia)
2. He is such a perv, he was totally trying to look down my butt crack or something.
3. Ew, his pant's are so low he's got crack.
4. So, you're gonna crack for a quid?
(So, you're gonna become a prostitute?)