From LQWiki

The term crack, in computing, usually involves breaking some form of security or protection.

It can refer to the use of an exploit or vulnerability to penetrate, disable or damage a computer system or application. It can also be the hack, exploitable vulnerability, or loophole that allows one to crack. A person who uses a crack in these meanings is a cracker. Not a hacker!!!

Cracking can also mean the action of removing the copy protection from a commercial program. People who write cracks consider themselves challenged by the copy protection measures. They will often do it as much to show that they are smarter than the developer who designed the copy protection scheme than to actually copy the program. Of course, crack can also mean the program, instructions or patch used to remove the copy protection of a program or to uncripple features from a demo/time limited program. A person who engages in these endeavours is also not a true hacker (although they may develop into one in time, as they leave their criminal past behind them). See also warez.

This article is based, in whole or in part, on entry or entries in the Jargon File.