Mountains
A mountain is any landform that rises 1,000 feet (300 meters) or more above the surrounding area.
Hills
Hills are smaller than mountains and are also not as steep. Although the heights of some hills might be close to some small mountains, their gently sloping nature prevents them from being a mountain.
Plains
Plains are kind of the opposite of mountains and hills. They are flat expanses of land with very little topographical change. There are high and low plains, depending on how and where they are formed.
Plateaus
A plateau is an elevated and primarily flat area of land with a border on at least one side with lower-lying land.