A Private Unblocking Key (PUK) code is a safety characteristic used to guard SIM playing cards from unauthorized use. When you enter your SIM card’s PIN (Private Identification Quantity) incorrectly thrice, your SIM card will likely be locked and you have to the PUK code to unlock it.
PUK codes are often supplied by the community operator, both on the SIM card packaging or in a separate letter. If you do not have your PUK code, you’ll be able to often get it by contacting your community operator’s customer support.