What is the term for a large area of flat land with few trees?

The term for a large area of flat land with few trees is "plain." Plains are characterized by their expansive, level surfaces which can stretch for miles and often have rich soil, making them ideal for agriculture. They are typically found in various climates and can be located near rivers or other bodies of water, which can contribute to their fertility.

Plateaus, while also flat, are elevated areas and are not synonymous with flat land when considering the term "few trees." Valleys are low areas between hills or mountains and are usually characterized by the presence of a water body and vegetation, rather than being flat and barren. Hills are raised areas of land with a sloping profile and do not fit the description of having flat land. Thus, the definition of a plain aligns perfectly with the description given in the question.