The load terminals on a charge controller power connected DC devices. The DC device must be compatible with the battery nominal voltage, and the battery bank capacity should be appropriately sized for the load. Loads can be many things from a DC refrigerator to a DC LED light.
Some loads should not be connected to the controller’s load terminals and instead connected directly to the battery. Highly inductive loads with high inrush currents may damage the controller’s load terminals. DC motors and inverters are examples.