This is called the false rejection rate, the rate at which the biometric systems denies an authorized user. This is better than the false acceptance rate in that this does not compromise the system. Allowing a unauthorized user makes a system compromised than rejecting a authorized user. VK* Should't it be called "False negative"? JW: I Agree, it should obviously be a "False Negative" based on the question being asked. The False Rejection Rate is an aggregation of multiple known False Negatives against the number of known successful authentications. The question however, only describes a single event, which is a "False Negative" and doesn't constitute anything close to a False Rejection Rate. I've edited the answers to reflect this. A False Negative is when the system rejects the correct person, and a false positive is when the system authenticates the incorrect person.