What is two$-$factor authentication?

the traditional security process, which requires a username and password

requires the user to provide two means of authentication: what the user knows $($password$)$ and what the user has $($security token$)$

requires more than two means of authentication such as what the user knows $($password$),$ what the user has $($security token$),$ and what the user is $($biometric verification$)$

the identification of a user based on physical characteristic such as a fingerprint, iris, face, voice or handwriting