The Sioux or Oceti Sakowin are groups of Native American tribes and First Nations people from the Great Plains of North America. The Sioux have two major linguistic divisions: the Dakota and Lakota peoples. Collectively, they are the Očhéthi Šakówiŋ, or "Seven Council Fires". The term "Sioux", an exonym from a French transcription ("Nadouessioux") of the Ojibwe term "Nadowessi", can refer to any ethnic group within the Great Sioux Nation or to any of the nation's many language dialects.

The Great Plains, sometimes simply "the Plains", is a broad expanse of flatland in North America. It is located just to the east of the Rocky Mountains, much of it covered in prairie, steppe, and grassland. It is the western part of the Interior Plains, which also include the mixed grass prairie, the tallgrass prairie between the Great Lakes and Appalachian Plateau, and the Taiga Plains and Boreal Plains ecozones in Northern Canada. Great Plains or Western Plains is also used to describe the ecoregion of the Great Plains, or alternatively the western portion of the Great Plains.