Crack generally means a licence number that has lots of extra goodies with e.g MBR infections, fake antimalware programmes, keyloggers, trojan downloaders etc...
It is an illegal way of using propriety software without paying. And is the most dangerous way to get anything
I would steer well clear of anything like that, unless you want to lose all your private data/money/credit rating and end up with a doorstop for a computer