2FA - Two factor authentication, you get asked a second secret besides your password. Banks used to give users a card with codes that you had to find and input when authenticating with them.

OTP - one time password, you receive a code over SMS or mail.

TOTP - Time based one time password, you have to have an authentication app that creates a clock based cryptographic code.

FIDO2 - fast identity online standard version 2, is a set of ID verification technologies. Usually you're asked to confirm access on another certified device. Like google asking you to check your phone for a notification when logging into a new browser.

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).