User authentication is the process of verifying the identity of a user before granting access to a system or application. This typically involves the user providing credentials, such as a username and password, which are checked against stored data to confirm their identity. There are various methods of user authentication, including multi-factor authentication, which adds an extra layer of security by requiring additional verification, such as a code sent to a mobile device. Effective user authentication helps protect sensitive information and ensures that only authorized individuals can access specific resources.