one type of trailer I have heard about and seen a couple of pictuers of (our firm used to run them) are what were nicknamed “cornish trailers” down here.
Basically there were tipper bodies that could be folded flat for carrying goods as a backload. i.e. tipper up, flatbed back.
I don’t think they are used much if at all now though
A reefer is a fridge trailer and the flat with the extra axles are used on container work. The trailer splits in two so that the front box can be unloaded
Cheers Lucy and Wheel Nut 
. There seems a
lot what as changed in the transport industry over
the years Wheel Nut and the Destination Doha dvd
was a eye opener watching the driver change truck
tyres and help stripping trailer brakes down ect.
that explains the very short trailers that i have seen with a 20 foot container on them. i always wondered why they were used. i didnt know they could be separated 
you live and learn