The term 'American Plain' refers to two distinct geographical regions in the United States. The first is the PRAIRIE, which is a large grassland area that stretches from the Rocky Mountains to the Mississippi River. It is characterized by flat or rolling terrain and is home to a variety of wildlife. The second region is the PAMPAS, which is a vast grassland region located in the southern part of South America. It is known for its rich soil and is an important agricultural region. Both the PRAIRIE and the PAMPAS are part of the American Plain and are important parts of the United States' natural landscape.