The Western United States (also called the American West, the Far West, and the West) is the region comprising the westernmost states of the United States. As American settlement in the U.S. expanded westward, the meaning of the term the West changed. Before about 1800, the crest of the Appalachian Mountains was seen as the western frontier. The frontier moved westward and eventually the lands west of the Mississippi River were considered the West.
The U.S. Census Bureau's definition of the 13 westernmost states includes the Rocky Mountains and the Great Basin to the Pacific Coast, and the mid-Pacific islands state, Hawaii. To the east of the Western United States is the Midwestern United States and the Southern United States, with Canada to the north, and Mexico to the south.
The West contains several major biomes, including arid and semi-arid plateaus and plains, particularly in the American Southwest; forested mountains, including two major ranges, the American Sierra Nevada and Rocky Mountains; the long coastal shoreline of the American Pacific Coast; and the rainforests of the Pacific Northwest.