Okay, so imagine you have a big, heavy box that you need to move from one place to another. But it's too heavy and too big to carry all at once.
A demountable rack offload and pickup system is like having a special machine that can help you move that big, heavy box in smaller parts.
Imagine the machine like a set of moving legs that can pick up the box and move it around. But instead of legs, it's a big metal frame with wheels that can drive to the box, pick it up and then drive it to where it needs to go.
The big metal frame is called a "rack" and it's designed to hold the box securely in place so it doesn't fall off while it's being moved.
When you need to move the box, you use the demountable rack offload and pickup system to pick it up and drive it to the new location. Once you get there, you lower the rack back down and take the box off piece by piece.
This makes it easier and safer to move big, heavy things without having to lift or carry them all at once.