A step deck (also called a drop deck) is a variation on the flatbed with two deck levels: a short upper deck over the gooseneck and a longer, lower main deck behind it. That lower deck lets taller cargo ride while staying under legal height limits.
It’s the go-to when freight is too tall for a standard flatbed but doesn’t need full heavy-haul equipment. Like a flatbed, it’s open for side or top loading and is common for machinery and other tall or oversized items.