A sound process
in which the sound is sent to four (or five, I forget which) channels around the listener to provide surround sound
. It has a fifth channel which is the subwoofer. I believe it is a predecessor to Dolby
How to tell if a recording of a song is in quadrophonic:
Easy. The name usually has Quad Mix beside the name, or you could check the liner notes.
The exponent of this technology is holophonics.