False rejection, also called a type I error, is a mistake occasionally made by biometric security systems. In an instance of false rejection, the system fails to recognize an authorized person and rejects that person as an impostor.
One of the most important specifications in any biometric system is the false rejection rate (FRR). The FRR is defined as the percentage of identification instances in which false rejection occurs. This can be expressed as a probability. For example, if the FRR is 0.05 percent, it means that on the average, one out of every 2000 authorized persons attempting to access the system will not be recognized by that system.
Compare false acceptance.