A prairie was a large flat expanse covered with grass.
In 1893, Samuel Clemens mused on the idea of space filled with multiple inhabited planets, imagining that man would become "lost in the vastness of the cosmic prairie". (TNG: "Time's Arrow")
Buffalo were native to Earth prairies in the United States of America. In 2266, Doctor Robert Crater wistfully recalled how the prairies used to be black with these creatures. (TOS: "The Man Trap")