Biometrics apply advanced digital methodologies, such as eye (iris and retinal) scan, ear and facial recognition, facial thermograms, speech recognition, fingerprint geometry and fingerprint matching. Other techniques include finger, foot, and palm prints, gait recognition, shoe wear pattern, DNA, voice analysis and recognition, hand writing, and more.

These principles can then be used, with the emphasis on establishing and verifying the genuine and unique identity of the individual concerned, for or applied in, use with multiple- and single-application smart cards, identity cards, access control to sensitive areas, forensic analysis, surveillance, monitoring, intrusion detection, personal financial services, border control, monitoring travel patterns, etc. 

The crucial element being that some complex biological parameters, unique to the individual, are being employed.