Ducted propeller

So imagine you have a toy airplane with a propeller that spins around and makes it go forward in the air. Now imagine instead of just the propeller being out in the open, it's inside of a tube or pipe called a duct. The duct goes all around the propeller, kind of like a tunnel, so that the air that the propeller pushes out gets directed more in one direction. This makes the airplane go faster and more efficiently because the air is being directed in a specific way. It's like when you blow up a balloon and let it go, the air pushes it forward because it's going in one direction. The ducted propeller works the same way except it's being pushed by the spinning propeller inside the tunnel.