USA stands for the United States of America, the country stretching across much of North America from the Atlantic Ocean to the Pacific Ocean. The USA includes 50 states, from Alaska in the far northwest to Hawaii in the Pacific, plus territories like Puerto Rico and Guam.

The country was founded in 1776 when thirteen British colonies declared their independence, establishing a form of government where citizens elect their leaders and the Constitution protects individual rights. Over the next two and a half centuries, the USA grew from those original thirteen states along the East Coast to span an entire continent.

The USA has been home to remarkable innovations: the airplane, the assembly line, the internet, and the moon landing, among countless others. Its culture has influenced the world through movies, music, technology, and sports. The country's motto, E pluribus unum, means “out of many, one,” reflecting how people from all over the world have come to the United States and become Americans.

When people say “the USA,” they're usually referring to the country as a whole, while “America” can mean the same thing or sometimes refers to the entire Western Hemisphere. You might see the abbreviation U.S.A. written with periods, or simply US when used as an adjective, as in “US history” or “US currency.”