Which of the following BEST describes using a smart card and typing in a PIN to gain access to a system?

Biometrics specifically refers to authentication using unique physical or behavioral characteristics such as fingerprints or retinal scans; a PIN and smart card combination does not involve any biometric measurement.

PKI (Public Key Infrastructure) is a framework for managing digital certificates and key pairs used in encryption and digital signatures; while smart cards can store PKI certificates, describing this scenario as PKI does not capture the authentication method being used.

Single factor authentication uses only one authentication factor category; this scenario uses two separate factor categories (something you have and something you know), which by definition makes it multifactor.

Multifactor authentication (MFA) requires a user to present credentials from two or more different factor categories: something you know (password/PIN), something you have (smart card/token), or something you are (biometric). A smart card is a possession factor and a PIN is a knowledge factor, satisfying the requirement for multiple distinct categories. This combination significantly increases security because an attacker would need to both steal the physical card and know the PIN.