small loudspeaker (earphone) held over the ear by a band or wire worn on the head. Headphones are commonly employed in situations in which levels of surrounding noise are high, as in an airplane cockpit, or where a user such as a switchboard operator needs to keep the hands free, or where the listener is moving about or wants to listen without disturbing other people. A headphone may be equipped with one earphone or two and may include a miniature microphone, in which case it is called a headset. For listening to stereophonically reproduced sound, stereo headphones may be used, with separate channels of sound being fed to the two earphones.