Multi-Factor Authentication (MFA) is a security system that requires you to provide more than one form of identification at the time of login to ensure you are who you claim to be. It is probably the most important first line of defence in cyber security.
It means users have to users at least two forms of authentication when logging in: something you know (e.g., a password) and something you have (e.g., a mobile phone or a code generator). In this way, even if someone steals your password, they cannot access your account unless they also have your mobile device or code generator in their possession.
Businesses as well as individuals should implement MFA wherever possible.