A Personal Identification Number (PIN) is a numeric code used to authenticate users during financial transactions or to grant access to secure systems. PINs are commonly associated with bank cards, where users must input their code at ATMs or point-of-sale terminals to complete a transaction. The typical PIN consists of four to six digits and serves as a security measure to protect against unauthorized access. In addition to banking, PINs are also used to secure mobile phones, computer accounts, and other digital services. The simplicity and effectiveness of PINs make them a widely used form of authentication.