2FA: two factor authentication. So using a password (something you know) in combination with something else, like something you are (biometrics) or something you have (security token, phone with authenticator app)
OTP: One-time password. A password you can only use once. Can be a list of passwords where you have to use the next one on the list with each login or any other mechanism that provides a unique password for each login.
TOTP: Time-based one time password. An OTP scheme where the password is derived from a shared secret and the current time. Like Google Authenticator.
FIDO2: Fast IDentity Online version 2. A standard that lets you use an authentication device to log into online services. This can be in the form of a USB key or something built into your computer (e.g. on a Mac you can use the built-in fingerprint scanner).