This is the way I understand it. In a semi floater the axle shaft and where the wheel studs mount is one piece. In a full floated the axle shaft connects to a locked hub or a drive plate. Then they both connect to the diff the same way. The full floater supports the weight on the axle housing, where the semi floater supports it on the axle shaft itself, thus making a full floater stronger.
The full floater is used on trucks that see more of a beating, the semi floater is common on normal 4x4s.
On this semi-floater you can see how the shaft and tube are 1 piece
Here on a full floater you can see how its seperate pieces