The Philadelphia accent is the accent of English spoken in Philadelphia and extending into Philadelphia's suburbs in the Delaware Valley and southern New Jersey. It is one of the best-studied dialects of American English due to the fact that Philadelphia's University of Pennsylvania is the home institution of William Labov, one of the most productive American sociolinguists. Unlike the dialects found in much of the rest of Pennsylvania, the Philadelphia accent shares several unusual features with the New York accent, although it is a distinct dialect region. The Philadelphia accent is, however, in most respects the same as the accents of Wilmington, Delaware and Baltimore, together with which it constitutes what Labov describes as the Mid-Atlantic States dialect region.
Actual Philadelphia accents are seldom heard nationally (Philadelphia natives who attain national prominence usually make an effort to tone down or eliminate distinctive pronunciations that would sound dissonant to non-natives). Movies and television shows set in the Philadelphia region generally make the mistake of imbuing the characters with a working class New York accent (specifically heard in Philly-set movies such as the Rocky series and A History of Violence) that is unlike how Philadelphians actually speak. A contrary example is the character of Lynn Sear (played by Toni Collette) in The Sixth Sense, who speaks with an accurate Philadelphia accent.
The use of geographically inaccurate accents is also true in movies and television programs set in Atlantic City (or any other region of South Jersey), where the characters are often imbued with a supposed "Joisey" accent, when in reality the New York-influenced dialect for New Jersey natives is almost always exclusive to the extreme northeastern region of the state nearest New York City. The dialect and accent for speakers in South Jersey is vastly similar to that of Philadelphians.
The precise realizations of features of the Philadelphia accent vary to some degree among different ethnic groups, social classes, and parts of the Philadelphia region. The general phonological features of the accent, however, are as follows:

Philadelphia is resistant to the cot-caught merger because the vowel phoneme of words like caught, cloth, and dawn is raised to a high [ɔ], increasing its distance from the [ɑ] of cot. Philadelphia shares this feature with New York and southern New England.
On is pronounced /ɔn/, so that, as in the South and Midland varieties of American English (and unlike New York and the northern U.S.) it rhymes with dawn rather than don.
The interjection "yo" was popularized (and possibly originated in its current meaning) in Philadelphia dialect among Italian American and African American Philadelphians. Today, Philadelphia natives in general are known to commonly use the interjection.
The words foreign, Oregon, origin, Florida, forest, horrible, quarrel, warren, and warranty are often pronounced with /ɑr/ rather than the /ɔr/ used in General American.
Both long -e and long -a sounds are shortened before -g. Eagle rhymes with "Iggle". League rhymes with big. Vague and plague rhyme with Peg. For some Philadelphians, colleague and fatigue also rhyme with big. But these are words learned later, so many use the standard American "coleeg" and "fateeg."
Many Philadelphians use the dark l in all positions.
Most Philadelphians have at least a little of an sh-sound instead of s-, especially before consonants.
In words like gratitude, beautiful, and prostitute, the "i" is pronounced with a long "ee" sound ([i]).