A biometric is the measurement of unique bodily features that is stored onto the computer to automatically recognise the person by scanning that particular body part like eye, fingerprint and face recognition. This helps as a security feature and allows authorization to only people having unique IDs

Example:
Nowadays, if you go to register for Aadhar or buy a new sim card, you will be asked to put your thumb print which then allows the computer to remember your identity in the future.
Similarly, smartphones nowadays scan your face and unlock phone