hopper or hopper car (rail)
(rail transportation) An open-top railroad car with sides and ends designed to transport free-flowing dry-bulk commodities. Hopper cars are loaded from the top and unloaded by gravity through funnel-shaped receptacles (hoppers) on the undercarriage of the railcar. Common commodities transported in hopper cars include grains, industrial minerals, plastic pellets, crushed rock, gravel, and sand. Hopper cars are available in open top and covered configurations. Covered hoppers often have sliding roofs for protection from the elements. Special interior linings are available to protect specialty commodities.