What is a large area of flat land or gently sloping land called?

A large area of flat or gently sloping land is known as a plain. Generally, plains are lowland areas that are less than 500 feet above sea level. They typically form by the deposition of sediment by water, wind or ice.

Plains often featured mostly grasses and few trees. The soil is often fertile, owing to deep sedimentary deposits and relatively minimal flora impact. Owing to this, plains are important to agriculture. A country's plains area is typically known as its breadbasket, as it produces a significant amount of food for the nation. Plains are also well-suited for livestock grazing.