Philadelphia, (commonly called Philly) and known as The City of Brotherly Love (from Greek: Φιλαδέλφεια, /fi.la.ˈðɛl.fja/, "brotherly love" from philos "loving" and adelphos "brother") is the fifth most populous city in the United States and the largest in population and area in the Commonwealth of Pennsylvania.

Philadelphia is coterminous with Philadelphia County.^GR6 The population of the city (at the 2000 census) is 1,517,550. Philadelphia is the second largest city on the U.S. East Coast (after New York City), and a major commercial and cultural center for the East Coast.

The Philadelphia metropolitan area is the fourth largest in the U.S. by the current official definition, with some 5.8 million people.

Philadelphia is one of the oldest and most historically significant cities in the United States. During part of the 18th century, the city was the second capital and most populous city of the United States. At that time, it eclipsed Boston and New York City in political and social importance, with Benjamin Franklin playing an extraordinary role in Philadelphia's rise.