Two-factor authentication (2FA), is an enhanced security mechanism that requires a computer user to have not just one, but two items in order to authenticate (sign-in).The first item is something you know, such as your typical password. The second item is something you have, such as a physical cell phone that an access code may sent to, or your fingerprint.One of the most common types of two-factor authentication is found with ATM machines, requiring you to have your PIN, something you know, and your bank card, something you have.