Definition

Biometrics is the science and technology of measuring and analyzing biological data. In information technology, biometrics refers to technologies that measure and analyze human body characteristics, such as DNA, fingerprints, eye retinas and irises, voice patterns, facial patterns and hand measurements, for authentication purposes.

Advantages of Biometrics

• Increase security - Provide a convenient and low-cost additional tier of security.
• Reduce fraud by employing hard-to-forge technologies and materials. For e.g.Minimise the opportunity for ID fraud, buddy punching.
• Eliminate problems caused by lost IDs or forgotten passwords by using physiological attributes. For e.g. Prevent unauthorised use of lost, stolen or "borrowed" ID cards.
• Reduce password administration costs.
• Replace hard-to-remember passwords which may be shared or observed.
• Integrate a wide range of biometric solutions and technologies, customer applications and databases into a robust and scalable control solution for facility and network access
• Make it possible, automatically, to know WHO did WHAT, WHERE and WHEN!
• Offer significant cost savings or increasing ROI in areas such as Loss Prevention or Time & Attendance.
• Unequivocally link an individual to a transaction or event.

Why are biometrics secure?

• Unique: The various biometrics systems have been developed around unique characteristics of individuals. The probability of 2 people sharing the same biometric data is virtually nil.
• Cannot be shared: Because a biometric property is an intrinsic property of an individual, it is extremely difficult to duplicate or share (you cannot give a copy of your face or your hand to someone!).
• Cannot be copied: Biometric characteristics are nearly impossible to forge or spoof, especially with new technologies ensuring that the biometric being identified is from a live person.
• Cannot be lost: A biometric property of an individual can be lost only in case of serious accident.

Only biometrics can verify you as you. Tokens like smartcards, etc.  aren't you and can be lost, stolen, duplicated (some) and forgotten.
Passwords aren't you and can be forgotten, shared, observed and broken.