Some articulated lorries have trailers that are called tilt trailers. What doe's tilt stand for?

It doe's not refer to a tilting body, i mean there like taughtliner trailers but the side posts come out and it can be stripped right down so it is like a flat-bed trailer & the tarp can be totally removed if needed. So you can load it from the top i.e. rolls of steel etc. I would love an answer? Thanx in advance. x-truka.