Authentication
The process of proving that a user, device, or system really is who or what it claims to be.
Authentication↗ is the process of proving that a user, device, or system really is who or what it claims to be, in short, confirming "who you are." Entering a password, approving a one-time code sent to your phone, or scanning a fingerprint are all authentication methods.
Proof of identity falls into three main factors: something you know (a password, a PIN), something you have (a phone, a hardware key), and something you are (biometric data like a fingerprint or face). Combining more than one of these factors is called multi-factor authentication (MFA), and it meaningfully increases security.
It is important to distinguish authentication from authorization↗, which determines what you can access: authentication confirms who walked through the door, while authorization determines which rooms that person may enter. Together, the two form the foundation of access security.