Deaf sounds refer to sound waves whose frequencies are above the human upper extremity (20,000 Hz). It is also called ultrasonic sound, auditory sound, etc. In English it is called "Ultrasound". The physical nature of audible words is no different than "normal" audible words, but people cannot hear them. Although the hearing range varies from person to person, the range of hearing in healthy adult youth ranges from 20 Hz to 20,000 Hz (20 kHz). Audible devices can operate at frequencies ranging from 20 kHz to multiple GHz (1 lakh Hz).

Deaf sound are used in many different cases. Objects are identified with auditory or ultrasonic instruments and distances are measured. In medicine, static or moving imaging of internal organs is widely practiced using methods called ultrasound imaging and ultrasonography. Invisible defects are detected with the naked eye using audible sound during non-destructive testing of manufactured goods and structures. In industry, audible noise is used for cleaning, mixing and accelerating chemical processes. Bats and babies (a type of porpoise or dolphin) use audible terms to determine the location of prey or obstruction.