Biometrics refer to the quantifiable data (or metrics) related to human characteristics and traits.  The quantifiable metrics can be gathered using various sensors and the collected data processed to identify individual persons.  Typically, biometric identifiers can be categorized as physiological and/or behavioral characteristics.  Generally, physiological characteristics are related to the shape of the body and can include (but not limited to) fingerprint, palm print, DNA, and scent.  In contrast, behavioral characteristics relate to a pattern of behavior and include (but not limited to) gait, voice, and typing rhythm.  Biometric identifiers can also include characteristics that are more subtle such as breathing patterns and heart rates.