Multi-factor authentication combines something you know, such as a password, with something you have, such as an authenticator app or security key, or something you are, such as a fingerprint. A stolen password alone is then not enough to sign in.
MFA blocks a large share of the account takeovers that hit small businesses, which is why regulators, insurers, and security frameworks increasingly require it. Authenticator apps and hardware keys are stronger than text-message codes. MFA should cover email, remote access, financial accounts, and any system holding client data.