Which identifier is used to uniquely recognize a user on a system?

• A. Username
• B. Password
• C. PIN
• D. Token

Answer: (A)

Identifying a user on a system is done with a username—the unique label associated with a specific account. The system uses this identifier to locate the correct account, apply the right permissions, and present the right resources. When you log in, you typically provide a username to tell the system which account to check, and then a password (or other credential) proves you are authorized to use that account. The other options—password, PIN, and token—are credentials or authentication factors used to prove who you are, not the identifier itself. A password or PIN is a secret that verifies identity, and a token is a proof of possession for multi-factor authentication; neither serves as the unique handle that distinguishes one user from another.