What does Biometric device mean?

Bio- refers to biological.

Metric - refers to measuring.

Biometric MEASURES something biological. In the case of a computer, it can digitize fingerprints, retinal scan, voice analysis... just about anything that might identify you as being unique from others.

Typically biometric devices are installed as a component of computer security, such as a fingerprint scan, a retina scan or a voice print.

In the case of a fingerprint scan, one would need to press on the pad that detects your fingerprint, and if it doesn't match, the computer will not allow you to have access to the computer.