Two-factor authentication is a method of electronic authentication that relies on two separate pieces of evidence to prove that a user is authorized to access a website or application.

The two pieces of evidence could be any of:
- Something the user knows, like a password.
- Something the user has, like a device or key.
- Something the user is, like a fingerprint or other means of biometric identification.
- The user's location, such as which network they are connected to.

The most common form of two factor authentication uses the first two forms of evidence: A password that the user knows, and a device that the user has.

Two-factor authentication can increase security: Even if a single form of authentication is stolen, such as a user's password or phone, an attacker cannot access the user's account. However, two-factor authentication is still vulnerable to phishing or man-in-the-middle attacks.
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