A long flat sled used for coasting down hills is called a toboggan.

Here are some other terms you might see used:

* Sled: This is a more general term that can refer to any type of sled, including toboggans.

* Snow tube: This is a large inflatable tube used for sliding down hills.

* Snowboard: This is a board with bindings used for sliding down hills.

Let me know if you have any other questions!