A valley. Depending on the formation it can also be a col /notch or saddle. Valleys will often be steep on both sides and or have a body of water passing through them.
Coastal Plain
A low lying land between hills or mountains is called a valley
A flat land surrounded by hills or mountains is called a valley.
Lower land between two mountains is called a valley.
They both are in between of mountains and hills
valley
The Great Plains is the huge expanse of flatlands from the Rocky Mountains eastward to the Mississippi River.
Depending on how far apart the mountains are, the low land could be called either a valley (for mountains that you can see on either side) or plains (in the case of the land between the Rocky Mountains and the Appalachian Mountains in The United States).
The great plains!
A mountain is something that is higher than the rest of the land. You can't be "higher than the rest of the land" unless there is lower land to be higher than. If there were no space between mountains, then all land would be at the altitude of the top of the mountains, and it would all be flat, and there would be no mountains.
No, Saskatchewan does not have any mountains. The landscape is flat with few trees and is called the prairies. Northern Saskatchewan is all forests and Southern Saskatchewan is flat land.
A low lying land between hills or mountains is called a valley