Explanation/Reference:
Biometrics refers to authentication techniques that rely on measurable physical characteristics that can be automatically checked.
Note: There are several types of biometric identification schemes:
face: the analysis of facial characteristics
fingerprint: the analysis of an individual's unique fingerprints
hand geometry: the analysis of the shape of the hand and the length of the fingers retina: the analysis of the capillary vessels located at the back of the eye iris: the analysis of the colored ring that surrounds the eye's pupil
signature: the analysis of the way a person signs his name.
vein: the analysis of pattern of veins in the back if the hand and the wrist voice: the analysis of the tone, pitch, cadence and frequency of a person's voice.
Reference: http://www.webopedia.com/TERM/B/biometrics.html