- Naturally occurring sediments that are produced by chemical actions resulting during the weathering of rocks. Clays are composed of hydrated aluminum silicates, such as Kaolinite, Illite, Palygorskite, Attapulgite, Bentonite, and Montmorillonite. Small amounts of other minerals can change the color (white, yellow, brown or red) and texture of the clays. Clays may include all earths that form a paste with water and harden when heated.
- Typically reserved to refer narrowly to the cultures of the native peoples of the United States and Canada, excluding the Eskimos and Aleuts. For the indigenous peoples of Canada use the term "First Nations." For the broader concept of the cultures of any native peoples of Central America, South America, North America, or the West Indies who are considered to belong to the Mongoloid division of the human species, use "Amerindian (culture)."
- Refers to the cultures of the continent of North America, which is bounded by the Atlantic Ocean, the Pacific Ocean, the Arctic Circle, and Central America. In classifications schemes based on physical geography, Central America, and North America are parts of the same continent.
- Limited to fragments of pottery or glass.