Philadelphia, colloquially referred to as Philly, and known as The City of Brotherly Love (from Greek: Φιλαδέλφεια, /fi.la.ˈdɛl.fɛj.a/, "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. The population of the city (at the 2000 census) is 1,517,550. According to the 2005 U.S. Census estimates, the city had a population of 1,463,281. [1] Philadelphia is the second-largest city on the U.S. East Coast (after New York City), and a major commercial, education, and cultural center for the nation.

The Philadelphia metropolitan area is the fourth largest in the U.S. by the current official definition, with some 5.823 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, and the second largest English speaking city in the world after London. 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.