Two-factor authentication

Two-factor authentication (2FA) adds an additional layer of security by requiring a time-based code from your authenticator app when you sign in. This helps protect your account even if your password is compromised. If enabled, when you login, you will enter your username and password as normal, but will then be prompted for a OTP code. Your authenticator app will provide that code.

To enable 2FA, to to your User menu > Account and click the Change button on the Two-Factor Authentication line. Once enabled, you will be given a list of recovery codes. Keep these somewhere safe, as you can use this to bypass the OTP in case your authentication app is ever disconnected, or lost. 

A good example of an authenticator app is 1Password.