A frontier is the political and geographical area near or beyond a boundary. A frontier can also be referred to as a "front". The term came from French in the 15th century, with the meaning "borderland"—the region of a country that fronts on another country. Unlike a border—a rigid and clear-cut form of state boundary—in the most general sense a frontier can be fuzzy or diffuse. For example, the frontier between the Eastern United States and the Old West in the 1800s was an area where European American settlements gradually thinned out and gave way to Native American settlements or uninhabited land. The frontier was not always a single continuous area, as California and various large cities were populated before the land that connected those to the East.

American pioneers also known as American settlers were European American, Asian American and African American settlers who migrated westward from the Thirteen Colonies and later the United States of America to settle and develop areas of the nation within the continent of North America.