The PIN acts like a password preventing other people from gaining unauthorized access to your device.
It is a numeric code which must be entered each time the device is started (unless the PIN security feature is turned off).
The PIN is associated with the SIM card (not the phone) and must be entered each time the phone is switched on. If a wrong PIN is entered three times in a row the handset is locked until you enter another code, called a PUK code.
Both the PINand the PUKcodes are supplied by giffgaff, but only the PIN code can be changed.