What is the meaning of PIN and PUK ?

 Personal Identification number (PIN) are given out with any new contract by telephone companies and others(e.g credit card companies). This secret number identifies the authorized owner of the cell phone and must be given each time  the phone is switched on. To prevent theft if the wrong PIN number is keyed in more than three times the telephone is locked. In this event, a number that is provided in the contract, the PUK (Personal Unblocking Key) is used to unblock the phone