what's the pin number?
A personal identification number sent to its user in a letter. The darkened paper flap prevents the number from being read by holding the unopened envelope to the light. A personal identification number (PIN, pronounced pin; often redundantly PIN number) is a numeric password used to authenticate a user to a system. PINs may be used with banking systems to authenticate the identity of the cardholder, but are also used in other, non-financial systems.