A Hopper.
A hopper car is a type of railroad freight car used to transport
loose bulk commodities such as coal, ore, grain,track ballast, and
the like. The name originated from the coke manufacturing industry
which is part of the steel industry This type of car is
distinguished from agondola car in that it has opening doors on the
underside or on the sides to discharge its cargo. The development
of the hopper car went along with the development of automated
handling of such commodities, with automated loading and unloading
facilities. There are two main types of hopper car: open and
covered.
Covered hopper cars are used for bulk cargo that must be
protected from the elements (chiefly rain) such as grain, sugar,
and fertilizer. Open cars are used for commodities such as coal,
which can get wet and dry out with less harmful effect. Hopper cars
have been used by railways worldwide whenever automated cargo
handling has been desired.