Modern sound-based
appliances often have a
button or
control to turn off the sound. This is great if, say, you've got the
volume on your
stereo or
tv cranked way up and you want to take a
phone call.
On an appliance like a telephone or speaker phone, the mute function works almost the exact opposite - it prevents the other party from hearing any sounds on your end.
Even the volume control in MS Windows has a mute option to silence any but the most basic computer-based noises. I'm always scrambling for this one when I come across a web site with tacky midis playing in the background.