A section is what you described.
A roomette was a room for one person--strikingly similar to today's Amtrak roomettes except for one not two, unless perhaps a mother and baby.
A double bedroom was a room for two. Daytime it could either be two chairs or one sofa. Bedrooms could sometimes be opened up en suite, space for four to sleep.
A compartment had two beds. By day there was both one sofa and one chair, strikingly similar to todays' bedroom, or deluxe bedroom as it was known until recenty. A little more floor room, though, I think.
A drwing room slept three people. I THINK sometimes there were three adult beds and sometimes two adult beds and one smaller bed. By day it had one sofa and two chairs.
A Master Room slept two, had three chairs during the day, and had a shower. Very few trains had master rooms. The Broadway Limited and the Crescent come to mind. Not many. This was normally the only shower on a train, and it was just for the occupants of this particular room. Very few public showers back then. The lounge car of the pre-Amtrak Sunset Limited had a public shower for sleeping car passengers only, not many more did.
I believe the pre-Amtrak California Zephyr had a shower in what it called a drawing room. Thus there could be some flexibility in the terms.
There was such a thing as a single bedroom. It was sort of a larger roomette, with more floor room, easier to lower and raise the bed during the night without backing into the aisle. Not many of these.
There were duplex roomettes, which were sort of staggered.
The above into is mostly from the 1959 Pennsylvnaia Railroad timetable.
Oh yes, in some cases a bedroom could be opened up en suite with a compartment, making for a quite nice and quite large accommodation.