The science of measuring physical aspects of people, and use it as identifiers. People do it all the time by identifying others by their voice, their face, their walk etc. Police do it with fingerprints, lip prints, palm prints etc. Hollywood agents do it with retinal scans. And this is where fiction starts to meet reality. There are many proposed technologies to validate a user by a machine that recognizes faces, fingerprints, retinas etc. So far, these have met with limited success, but they are improving. The real problem is that they are really only secure when supervised by a human, thus they will likely not replace other technologies for internet shopping etc in the short run.
Set of identification and authentication techniques based on the recognition of characteristics one has (fingerprints, hand shape, iris or retina patter, etc.) or learns (keyboard typing , signature, speech).