A stacker is a piece of equipment that takes washed gravel waste and dumps it into a waste pile, moving material from low to dropping it from on high.
Most washplants have integral stackers to pile up the tailings. Accessory stackers provide additional clearance, height, reach, and can be fed by the stacker. Rotational stackers can rotate along a path and pile up waste into a circular berm instead of a conical pile.
The opposite of a stacker is a feeder, such as hopper feeders.