A flatcar is a train car that has a flat surface on top instead of walls or a roof. It's like a big, long, wide board that can be used to carry all sorts of things like big machines, lumber, or even other train cars. The flat surface makes it easy to load and unload things from the car, and the car can be pulled by a locomotive to transport the things to different places. Flatcars can be used for all kinds of transportation needs, like moving heavy equipment for construction or carrying cargo across the country. They're really useful for getting big, bulky items from one place to another!