Biometric describes machines and computer systems that measure a living body in order to check who someone is. The usual measurements are fingerprints, the face, the iris of the eye, sometimes the voice or the way a person walks. Those measurements are kept on a computer and then matched later — at an airport passport gate, on a phone lock, at an office door. You will see biometric passport, biometric scan, biometric data. It is a describing word in those phrases, and people also say biometrics as a noun for the whole method. The tone is official and technical, not warm. Though actually, an older scientific use of biometrics meant the statistics of living measurements — heights, harvests, and so on. That meaning is still in some research papers. In ordinary life now, the word almost always points to identity machines.