**BER** is short for **b**it **e**rror **r**ate.

In a digital transmission, BER is the percentage of bits with errors divided by the total number of bits that have been transmitted, received or processed over a given time period. The rate is typically expressed as 10 to the negative power.

For example, four erroneous bits out of 100,000 bits transmitted would be expressed as 4 x 10^{-5}, or the expression 3 x 10^{-6} would indicate that three bits were in error out of 1,000,000 transmitted. BER is the digital equivalent to signal-to-noise ratio in an analog system.

*See also BERT.*