It is the process of determining whether a user is who they say they are.
Its most common form of authentication and its the least secure as it only requires username and password to gain full acess to the system.
It add an additional layer of verification to identify valid user so its harder to break. It require username , password as well as additional piece of identifying information such as one-time password, biometric, SMS code etc.
With this user login on one application and get access to many other applicaitions. Organizations can accomplish this by identifying a central domain (most ideally, an IAM system) and then creating secure SSO links between resources.
It uses more system--irrelevant factors to legitimize users. Like 2FA, MFA uses factors like biometrics, device-based confirmation, additional passwords, and even location or behavior-based information (e.g., keystroke pattern or typing speed) to confirm user identity.