Bit Error Rate (BER) is a measure of the number of errors in a transmission system compared to the total number of bits sent. It is expressed as a ratio, often represented in scientific notation, such as 1 x 10^-6, indicating one error for every million bits transmitted. A lower BER signifies a more reliable communication system. BER is crucial in evaluating the performance of various communication technologies, including wireless networks, fiber optics, and satellite communications. Engineers use BER to assess and improve the quality of data transmission, ensuring that information is delivered accurately and efficiently.