Power Gating is a technique used in integrated circuit design to reduce power consumption, by shutting off the current to blocks of the circuit that are not is use.
Power gating is used to save the leakage power when the system is not in operation. This is accomplished by adding a switch either to VDD or VSS supply. When the design is power gated it literally means the block is powered OFF. Powering OFF a design block is the most beneficial technique of all the low power techniques because you dissipate near zero power. Near zero because the switching circuit used for implementing power gating still dissipate leakage power even in power gating mode. The control to the power gating switching circuit is generated by the Power gating control block.