Beat is the term related to sound waves. Beat frequency is nothing but the difference in frequency of two wave. It is due to the destructive and constructive interferences. When two sound waves of different frequency approach your ear, the alternating constructive and destructive interference causes the sound to be alternatively soft and loud - a phenomenon which is called "beating" or producing beats. The beat frequency is equal to the absolute value of the difference in frequency of the two waves. The number of beats per second is equal to the difference in frequency. According to these interferences, sound will be soft or loud. Actually beat frequency is the absolute value of the difference in wave frequencies. The formula for the beat frequency is,
are frequency of two waves.