A full float axle uses hubs to support the weight of the vehicle.
The axle shaft bolts to the out side of the hub. That way, the shafts only transmit rotational torque, but does not take on the dutys of supporting the vehicle weight. These are generally found in 3/4 ton and bigger trucks because of their obvious load carying capabilities.
A semi float uses the axle shaft to support the weight of the vehicle as well as transmit rotational torque. The shaft runs in a set of bearings at the end of the axle housing that take the weight of the vehicle.
A full floater is easy to spot, just look for the hub sticking out from the center of the wheel. Not a chrome center cap, but a hub with the axle shaft bolted to it.