The United States of America (USA), commonly known as the United States (U.S.) or America, is a federal republic composed of 50 states. 48 of them are joined together to make up the contiguous United States. These states, called the “lower 48”, can all be reached by road without crossing a border into another country. They go from the Atlantic in east to the Pacific in the west.

At 3.8 million square miles (9.8 million km²) and with over 325 million people, the United States is the world’s third- or fourth-largest country by total area and the third-most populous.

The U.S. territories are scattered about the Pacific Ocean and the Caribbean Sea, stretching across nine official time- and diverse climate zones.

The United States is a highly developed country, with the world’s largest economy by nominal GDP and accounting for approximately a quarter of global GDP. The U.S. economy is the fastest-growing at the American continent and it is largely postindustrial, characterized by the dominance of services and knowledge-based activities.