The United States of America (abbreviated USA), also called United States (abbreviated U.S., US) and often colloquially shortened to America, is a federal republic. It consists of 50 states, a federal district (the capital Washington, D.C.), five major territories and several island territories. The 48 contiguous Continental United States (often called the Lower 48) and Alaska are in North America, while Hawaii and smaller outlying territories are in the Pacific and Caribbean, respectively. The country has very high geographic and climatic diversity with a wide variety of animal and plant species.

The United States of America is the third largest country in the world by area, 9.83 million square kilometers (after Russia and Canada), and by population, about 328 million (after China and India). The largest city by population is New York City; major metropolitan areas include Los Angeles, Chicago, Dallas, Houston, Philadelphia, Washington, Miami, Atlanta, Boston and San Francisco, each with more than 5 million residents.

Source: Wikipedia