Two-factor authentication (2FA) is an extra layer of security that requires two distinct forms of identification in order to gain access to an online account or computer system. In this context, a factor means a way to convince the account or system that you are who you say you are.
In 2FA, the first factor is typically your username/password pair. The second factor may be something you have (such as a text with a time-based code sent to your smartphone or other device, or a smartphone authenticator app) or something you are (biometrics using your fingerprint, face, or retina). Despite the slight inconvenience of a longer log-in process, security experts recommend enabling 2FA wherever possible.