Two-factor authentication (2FA) is an identity and access management security method that requires two forms of identification to access resources and data. The first factor you provide is a password (often referred to as something you know.)   In addition to the password, you must provide another form of identification that is not memory dependent (often referred to as something you have, such as a smartphone or a physical token.) By simply enabling 2FA on your accounts, you gain an additional layer of security beyond just a password.

Source: Tripwire – The State of Security