Which authentication method requires a biometric characteristic?

The authentication method that involves a biometric characteristic is "what you are." This approach relies on unique physical traits of an individual, such as fingerprints, facial recognition, voice patterns, or iris scans. These biometric identifiers are inherently tied to the individual and provide a high level of security because they are difficult to replicate or steal compared to passwords or physical keys.

In the context of security practices, biometric authentication is praised for its ability to ensure that access is granted only to those who bear the correct physiological traits, thereby enhancing overall security. It also offers convenience since users do not need to remember passwords or carry security tokens; they simply need to present their biological characteristic.

The other methods mentioned, such as something you know (like a password), something you have (such as a security token or card), and the concept of forgetting (often a trick option in this type of question), do not involve biometric characteristics. Therefore, the focus on unique physical traits makes "what you are" the appropriate choice for this question.