Dolby Surround is the consumer version of the original Dolby multichannel analog film sound format Dolby analog and Dolby SR (Spectral Recording). When a Dolby Surround soundtrack is produced, four channels of audio information (Left, Center, Right and Mono) surround are matrix-encoded onto two audio tracks. These two tracks are then carried on stereo program sources such as videotapes and TV broadcasts into the home, where they can be decoded by Dolby Pro Logic to recreate the original four-channel surround sound experience.
With the introduction of the Dolby Digital multichannel film sound format, Dolby Digital has replaced Dolby Surround as the preferred technology to deliver multichannel audio to consumers via DVD-Video, digital television, and games. [Source: Dolby Technologies]