The term USA PART is an acronym for United States of America, which is the official name of the country commonly referred to as America. The United States of America is a federal republic composed of 50 states, a federal district, five major self-governing territories, and various possessions. It is the world's third-largest country by total area and the fourth-most populous country. The capital of the United States is Washington, D.C., and the largest city is New York City. The United States is a highly developed country and has the world's largest economy by nominal GDP and second-largest economy by PPP, accounting for approximately a quarter of global GDP.