Philadelphia English is a variety or dialect of American English native to Philadelphia and extending into Philadelphia's metropolitan area throughout the Delaware Valley and South Jersey, including Atlantic City and Wilmington, Delaware. Philadelphia English is one of the best-studied types of English, as Philadelphia's University of Pennsylvania is the home institution of pioneering sociolinguist William Labov. Philadelphia English shares certain features with New York City English and Midland American English, although it is a distinct dialect. The closest relative of the Philadelphia accent is the Baltimore accent, both of which constitute what Labov describes as a single "Mid-Atlantic" regional dialect.