(travel,informal) A class of accommodation, typically on trains, which is less comfortable than other classes, and might have wooden seating.
1962 December, “Beyond the channel: U.S.S.R.: Train speeds still rising”, in Modern Railways, page 418:
One main line only can show any mile-a-minute running, and that is the straight and reasonably level 404 miles between Moscow and Leningrad. There are two diesel-hauled expresses in each direction daily—rather oddly carrying "hard class" passengers only—which cover the distance in 6hr 20min [...].
