5.1 channel digital surround sound 
The popular digital surround-sound technique used by Dolby Digital technology in which audio is recorded on six, or 5.1, separate tracks: front left, front right, front center, rear left, and rear right, with an extra track (the .1) reserved for very low bass. This method (also called AC-3) mimics the three-dimensional quality of sound in real life and has become ubiquitous in home-theater systems. Although analog surround sound such as Dolby Pro Logic also often uses six speakers, the analog format simply splits a traditional stereo signal into front and rear components.