False reject rate (FRR): This is commonly referred to as a Type I error, or a false rejection error.
False accept rate (FAR): This is commonly referred to as a Type II error, or a false acceptance error.
Crossover error rate (CER): This is a measurement betwee then the FRR and FAR represented as a number or a percentage.  The lower the number or percentage, the more accurate the biometrics system is.  For example, a  CER of 2 (or 2 percent) is much better than a CER of 10 (or 10 percent).