Audio Frequency-Shift Keying (AFSK) is a digital modulation technique used to transmit digital data over audio channels. It involves shifting the frequency of an audio carrier signal between two distinct frequencies to represent binary 0 and 1. AFSK is commonly used in applications with limited bandwidth, such as amateur radio, radio telemetry, wireless modems, and digital data transmission over telephone lines. It is valued for its simplicity, narrow bandwidth, and compatibility with existing audio communication systems, making it robust against noise and interference in certain communication scenarios. However, it may be relatively slower compared to other digital modulation techniques.