Biometric identifiers are generally divided into two main categories: (PDF) An introduction to Biometrics - ResearchGate

The Science of Identity: An Introduction to Biometrics Biometrics is the automated recognition of individuals based on their unique biological and behavioral characteristics. Derived from the Greek words bio (life) and metrics (to measure), this field has evolved from traditional fingerprinting into a cornerstone of modern digital security. Core Categories of Biometric Traits