PUK is the code required to unlock a GSM SIM card that has disabled itself after an incorrect PIN code was entered 3-5 times in a row.
If an incorrect PUK code is entered a certain number of times (typically 5-10), the SIM card will permanently block (disable) itself.
You must contact the carrier (service provider) that issued the SIM card to obtain the PUK code. (We don't have it. Please don't ask.)