A Personal Unblocking Key (PUK) code is a security measure used by mobile network operators to protect SIM cards from unauthorized use. If you enter an incorrect PIN code three times, your SIM card will be blocked and you will need to enter the PUK code to unblock it.
PUK codes are typically provided by your mobile network operator when you purchase a new SIM card. You can also find your PUK code by logging into your online account or by contacting customer service.