What does "two-factor authentication" require?

Two-factor authentication requires two different forms of identification to verify a user's identity before granting access to a system or service. This approach adds a significant layer of security by combining something the user knows (like a password) with something the user has (such as a smartphone or a hardware token) or something the user is (like a biometric feature). By requiring these two different factors, it mitigates the risk of unauthorized access, even if one factor, like a password, has been compromised.

The other options do not meet the criteria of two-factor authentication. A single password does not provide enough security by itself, as it relies solely on knowledge. A biometric scan alone only counts as one form of identification, failing to meet the two-factor requirement. Similarly, using only email confirmation lacks the necessary diversification of authentication methods, depending solely on one type of identification.