2FA stands for 2 Factor Authentication. It is used in order to place an additional element of security over your Plutus accounts. 2FA is optional, though we highly recommend enabling it.
In addition to your password you will be required to use an authentication application on your smartphone or mobile device in order to prove your identity when logging in. This can prove very helpful in a situation where your personal login details are compromised.
For instructions on how to set up 2FA, click here