Sucks that I have to preface but people can be jumpy here. This is genuine curiosity, I'm actually asking, because it's really probably something I should already know. Can you explain the nuance to me please?
My understanding, speaking mostly of apps/websites, I know jobs can be much different:
Most places have the first factor as a password.
First factor (or "login") = username+password pair.
For the longest time that was all there was, "your login" was just a login, which meant a username and password combination. Then 2FA/MFA ("2 factor authentication / multi-factor authentication") came along in the form of username+password combo plus SMS/email/Google Authenticator/Yubikey/etc to verify as the 2nd form of authentication. You can have 3FA 4FA 5FA whatever if you want and if it's supported by the app/website. So 2FA is MFA, but MFA is not necessarily 2FA.