In a Surround Sound system with either two Rear Channels, also known as Surround Channels, the Channel intended to go behind the listener and to his left is the Left Surround Channel. In a three Rear Channel configuration this channel is normally positioned directly to the left of the listeners, but is still called Left Surround.
If there are more than three Surround Channels there may be two or more Left Surround Channels, with names like Left Surround Diffuse and Left Surround Direct. For systems with only a single Surround Channel no designation of left or right is necessary.
The Left Surround Channel may be referred as simply Left Surround, as in the Channels are Left, Right, Center, Left Surround, and Right Surround.
The image below shows the position of the Left Surround Channel in a 5.1 Surround Sound configuration.