In a Surround Sound system there is typically a single Channel positioned directly under the center of the screen. This is called the Center Channel. The Center Channel is typically used mostly for dialog, with music and positional effects being provided by some combination of standard Left Channel and Right Channel speakers, and one or more Surround Channels.
The Center Channel may be referred as simply Center, as in the Channels are Left, Right, Center, Left Surround, and Right Surround.
The image below shows the position of the Center Channel in a 5.1 Surround Sound configuration. The position should be the same in all Surround Sound configurations.