what is password CRACKER?  

actually the question was wrong little bit... but there is cracking word use for carcking a software by means of a small tool.. examplae when a game is pirated they use some small icon to replace which can make the game to run... or a key gen took to activate a software that makes the programm to run. hacker is nothing but the peron who does it and those cracking comes under hacking hope u understand a little bit wat i was tryiing to say :)

What you asked i think to crack any password, and there are number of things in which some are effective and some are not.
generally a hacker looks for your personal information to crack it.
and the other and sured way is the brute force attack, which use all the possible words to crack the password but this is not effective enough if your password is long and have alphabet numeric and symbols all. it could take even years to crack password by using a normal pc.