What is a biometric feature, and what is its main drawback for authentication?

A biometric feature is a unique, measurable physical characteristic of a human that can identify the person, physiological (fingerprint, face geometry, iris, hand geometry, vein pattern, DNA) or behavioural (signature, typing speed, gait, voice); its main drawback is that, once compromised, it cannot be revoked or regenerated the way a password can.

Ordinary physical features such as height or eye colour are not biometric; they are not unique enough.

Go deeper:

• Biometrics (Wikipedia) — the modalities and why a compromised biometric cannot be reissued.