Bit Error Rate. The number of bit errors that occur within the space of one second. This measurement is one of the prime considerations in determining signal quality. The higher the Data Transmission rate the greater the standard. A DS-1 signal is considered acceptable with a BER of 10-6, but an OC-3 signal requires a BER of no more than 10-12.

In Telecommunication transmission, the Bit Error Rate (BER) is the percentage of bits that have errors relative to the total number of bits received in a transmission, usually expressed as ten to a negative power. For example, a transmission might have a BER of 10 to the minus 6, meaning that, out of 1,000,000 bits transmitted, one bit was in error. The BER is an indication of how often data has to be retransmitted because of an error. Too high a BER may indicate that a slower Data Rate would actually improve overall transmission time for a given amount of transmitted data since the BER might be reduced, lowering the number of packets that had to be resent.

A BERT (bit error rate test or tester) is a procedure or device that measures the BER for a given transmission.