Biometrics (ancient Greek: bios ="life", metron ="measure") is the study of methods for uniquely recognizing humans based upon one or more intrinsic physical or behavioral traits.

In information technology, biometric authentication refers to technologies that measure and analyze human physical and behavioural characteristics for authentication purposes. Examples of physical (or physiological or biometrc) characteristics include fingerprints, eye retinas and irises, facial patterns and hand measurements, while examples of mostly behavioural characteristics include signature, gait and typing patterns. All behavioral biometric characteristics have a physiological component, and, to a lesser degree, physical biometric characteristics have a behavioral element.

In a typical IT biometric system, a person registers with the system when one or more of his physical and behavioural characteristics are obtained. This information is then processed by a numerical algorithm, and entered into a database. The algorithm creates a digital representation of the obtained biometric. If the user is new to the system, he or she enrolls, which means that the digital template of the biometric is entered into the database. The process of converting the acquired biometric into a digital template for comparison is completed each time the user attempts to authenticate to the system. The comparison process involves the use of a Hamming distance. This is a measurement of how similar two bit strings are. For example, two identical bit strings have a Hamming Distance of zero, while two totally dissimilar ones have a Hamming Distance of one. Thus, the Hamming distance measures the percentage of dissimilar bits out of the number of comparisons made. Ideally, when a user logs in, nearly all of his features match; then when someone else tries to log in, who does not fully match, and the system will not allow the new person to log in. Current technologies have widely varying Equal Error Rates, varying from as low as 60% and as high as 99.9%.