2FA / MFA
Two- or multi-factor authentication — you have to prove who you are with two independent things.
A password (something you know) plus a code from your phone, a security key, or your fingerprint (something you have or are). The idea is that even if someone steals your password, it isn't enough to get in.
Common forms: SMS code (vulnerable to SIM-swap), TOTP app like Authy or Google Authenticator (better), and hardware keys like YubiKey (best).