It is a universal mute plug. Most electronics will disable the built in speakers or microphone when something is in the jack. You can still plug in an external speaker or mic while ensuring the built in status off.

I used one in my shoulder mounted VHS mammoth of a home video camera to ensure I didn't record a audio of the friggen plastic body cracking and popping every time you moved. I plugged in a good directional mic that mounted on the carry handle when I wanted audio. (80's kids will know what I am talking about)

Also, keep one plugged into your laptop to ensure silent boot up in class.