Surround sound is a term applied to several types of processes that enable the listener to experience sound coming from all directions, depending on the source material.
Getting Surroud Sound - The AV Receiver
To get surround sound, you need a component that can decode and reproduce surround sound from a source, such as a DVD. Most commonly, this component is referred to as an AV Receiver (Audio/Video Receiver), Home Theater Receiver, or Surround Sound Receiver.
A Preamplifier that switches and controls which audio and video source is selected (such as a DVD player, VCR, CD player, etc...) and processes the incoming stereo or surround sound signals and distributes them to the correct amplifier channels and the subwoofer output.
A built-in Multi-channel amplifier (5.1, 6.1, or 7.1 channels) that sends the surround sound signals and power to the speaker system.