Definition of prairie:
1: land in or predominantly in grass
2: a tract of grassland: as
a: a large area of level or rolling land in the
Mississippi River valley that in its natural uncultivated state usually has deep fertile soil, a cover of tall coarse grasses, and few trees
b: one of the dry treeless plateaus
east of the Rocky Mountains that merge on their east side with the prairies proper and are characterized by shorter grasses and drier less fertile soil
First Known Use: circa 1682
http://www.merriam-webster.com/dictionary/prairie