Biometrics refers to technologies used to detect and recognize human physical characteristics. In the IT world, biometrics is often synonymous with "biometric authentication," a type of security authorization based on biometric input.
There are several types of biometric authentication. Common examples include fingerprint scanning, retinal scanning, facial recognition, and voice analysis. A facial recognition system, for instance, uses a camera to capture an image of a person's face. The photograph is then recorded and processed using biometrics software. The software attempts to match the scanned image with an image from a database of users' photos. If the scan is close enough to a specific user, the person will receive authorization to continue.
In many cases, a biometric scan is similar to a login. For example, some computers have a finger scanner that allows you to authenticate yourself by swiping your finger across a sensor. Instead of entering a username and password, the finger scan provides your authorization. Some retail outlets now use finger scanners to verify people's identity as an alternative to entering a unique pin number. High-security government and office buildings may even require retinal scans in order to access certain areas of the building. In some cases, a keycard, passcode, or login is required in addition to a biometric scan in order to provide extra security.