AF meaning in Electronics ?

An audio frequency or audible frequency (AF) is a periodic vibration whose frequency is in the band audible to the average human, the human hearing range. The SI unit of frequency is the hertz (Hz). It is the property of sound that most determines pitch.

The generally accepted standard hearing range for humans is 20 to 20,000 Hz. In air at atmospheric pressure, these represent sound waves with wavelengths of 17 metres (56 ft) to 1.7 centimetres (0.67 in). Frequencies below 20 Hz are generally felt rather than heard, assuming the amplitude of the vibration is great enough. High frequencies are the first to be affected by hearing loss due to age or prolonged exposure to very loud noises.