Biometrics are not usernames. They are physical identifiers and unlike usernames you can’t change them.

I used to work in a datacenter that required you to go through a mantrap to access. It required three things:

1. Something you have (a card key)
2. Something you know (a PIN)
3. Something you are (biometrics)

To get to the datacenter floor you use a card key to open the door to the mantrap. It’s a small vestibule about the size of a phone booth. Once inside the door closes. You then enter your PIN on a keypad and place your hand on a biometric scanner. Once your hand is recognized the inner door opens and lets you into the datacenter. I was told the mantrap also weighed you and compared that with previous trips through to make sure somebody else didn’t sneak through with you.