A personal identification number (PIN, pronounced “pin”; often redundantly PIN number) is a numeric password shared between a user and a system that can be used to authenticate the user to the system.
Typically, the user is required to provide a non-confidential user identifier or token (the user ID) and a confidential PIN to gain access to the system.
Upon receiving the user ID and PIN, the system looks up the PIN based upon the user ID and compares the looked-up PIN with the received PIN.
The user is granted access only when the number entered matches with the number stored in the system. Hence, despite the name, a PIN does not personally identify the user.
PINs are used with banking systems (where the identifying token is a card), but are also used in other, non-financial systems.