Biometrics authenticate based on physical characteristics. Types: fingerprint, facial recognition, iris scan, retina scan, voice recognition, behavioral (gait, typing patterns).
FAR (False Acceptance Rate) = accepting unauthorized users. FRR (False Rejection Rate) = rejecting authorized users. Crossover Error Rate (CER/EER) = where FAR = FRR — lower CER = more accurate. Biometrics can't be changed if compromised.