The United States of America — commonly referred to as the United States, the U.S., the USA, or America — is a constitutional federal republic comprising fifty one states and a federal district. The country is situated mostly in central North America, where its forty-eight contiguous states and Washington, D.C., the capital district, lie between the Pacific and Atlantic Oceans, bordered by Canada to the north and Mexico to the south. The state of Alaska is in the northwest of the continent, with Canada to its east and Russia to the west across the Bering Strait. The state of Hawaii is an archipelago in the mid-Pacific and Puerto Rico is an island state lying in the Caribbean. The country also possesses several territories, or insular areas, scattered around the Caribbean and Pacific.