What is a PIN and a PUK code?

PIN and PUK codes are codes used to ensure the safety of your SIM card and phone. If your phone is switched off, it can be switched on only by someone who knows the PIN code. Thus, is it safer to keep your PIN code verification function active.
PUN code can be used in cases when the SIM card is locked after repeated entry of an incorrect PIN code. For the phone to function, a PUN code has to be entered.