Just went through booking a sleeper train in Poland and found 4 person Couchette and 6 Person Couchette.
Seat 61 has probably the best description of the compartment that I have seen.
What are couchettes?
Couchettes are basic, inexpensive sleeping accommodation, with 6 bunks per compartment. On many routes you can also choose to travel in a less-crowded 4-berth compartment, for only a few euros more. By day, a couchette compartment is an ordinary seating compartment, with three-a-side bench seats facing each other (the picture of the French couchette below shows the middle bunk lowered to form the seat back in daytime mode). At night, the seats convert to bunks. Each bunk is basically a padded ledge supplied with pillow, sheet and blanket which you arrange yourself. Each berth has its own reading light. Washrooms and toilets are available at the end of the corridor. The sexes are normally mixed in couchettes, as you do not normally fully undress, but on many routes women can ask for a berth in a ladies-only compartment. Couchette cars come in many different designs, all based on the same format. Here are some some German City Night Line ones:
Apparently some trains, to the best of my understanding within Poland Only, provide Cheap or Cut-Price Couchette the difference between the regular and cut-price is linen, from intercity.pl:
With a Cut-Price Couchette, passengers travel in a couchette compartment furnished with six berths. Bedding is not provided, but the price includes a disposable sheet. Cut-Price Couchette tickets can be purchased at ticket offices, from the conductor and online.