What is a RSD? 

RSD means “Roller Shutter Door”

What is a Dock Leveller?

Dock levellers are also called loading docks. Not all trucks are the same height, and the height of the trailer floor within a truck can vary according to how heavily the truck is laden. Thus there is not only a gap to bridge but a height difference to overcome. Various devices are employed in order to achieve this: dock plates, dock levelers, dock boards, and various forms of lift. These devices vary in construction, suitability to dock conditions, cost of installation, and loading capacity.

Dock levelers and lifts are generally permanent fixtures at each door of a dock. Dock plates and dock boards are generally, by contrast, portable, and not fixed either to dock or truck. Dock leveler

What is the difference between a HPD and HSD?

HPD is a high performance door, HSD is a high speed door. Technically, they are the same thing, just different names. Some other names include fabric doors, automatic doors or high-speed roller doors.