Stands for "Personal Unlocking Key Code." A PUK code (or just "PUK") is an 8-digit code used to unlock a locked SIM card. It is similar to a "password reset" in that it resets the SIM card PIN and allows you to choose a new one.
The PUK is typically printed next to the default PIN on the larger card that came with your SIM card. If you cannot find the PUK code, your wireless carrier may be able to provide it.
SIM Card PIN
The 4-digit PIN prevents unauthorized use of a SIM card. You may need to enter the PIN when you activate a new phone, install a new SIM card, or transfer a SIM card to another phone. Depending on your smartphone's settings, it may require you to enter the PIN each time you start your phone. You can typically change the PIN on a mobile device by going to in the device settings.
If you enter your PIN incorrectly three times, you must enter the correct PUK to unlock the card. If you enter the wrong PUK code 10 times, the SIM card will become permanently locked, and you will need to replace it.
NOTE: A PUK may also be called a PUC, or Personal Unblocking Code.