In StarCraft II, a Supply Depot allows Terran units to enter and leave a fortified wall when lowered or raised.
Terran players commonly use Supply Depots as part of wall-in designs at a ramp or narrow entrance. A raised Depot blocks movement, while a lowered Depot permits friendly units and selected battlefield traffic to pass. This makes the structure useful for controlling access as well as providing supply.
The mechanic is particularly important early in a match, when Terran players may want to delay enemy ground units while keeping their own infantry able to move through the base entrance. Several Depots can be arranged with other Terran structures to create a controllable barrier.
A Bunker provides defensive firing positions but is not the standard structure used to open and close a wall. A Command Center is a main base structure, while a Barracks produces infantry. The Depot's supply function and terrain-control function are separate roles.