A railyard is a building where freight cars are built in the game of Imperialism.
It appears near the right-hand side of the "Give Industry Orders" screen. Rail tracks extend off the map and through the industrial areas. Part-way through the game it expands to accommodate materials from villages and later goods from towns, but the expansion is purely superficial: you still have to build freight cars to bring in the extra commodities.
Building a freight car requires two labor units and one each of coal and steel.