https://en.wikipedia.org/wiki/Plain
In geography, a plain is a flat expanse of land that generally does not change much in elevation, and is primarily treeless.Plains occur as lowlands along valleys or at the base of mountains, as coastal plains, and as plateaus or uplands.. In a valley, a plain is enclosed on two sides, but in other cases a plain may be delineated by a complete or partial ring of hills, by mountains, or by …