The definition of pop music is purposefully flexible as the music that is identified as pop is constantly changing. At any particular point in time it may be easiest to identify pop music as that which is successful on the pop music charts. For the past 50 years the most successful musical styles on the pop charts have continually changed and evolved. However, there are some consistent patterns in what is identified as pop music.
Pop Vs. Popular Music
It is tempting to confuse pop music with popular music. The New Grove Dictionary Of Music and Musicians, the musicologist's ultimate reference resource, identifies popular music as the music since industrialization in the 1800's that is most in line with the tastes and interests of the urban middle class. This would include an extremely wide range of music from vaudeville and minstrel shows to heavy metal. Pop music, on the other hand, has primarily come into usage to describe music that evolved out of the rock 'n roll revolution of the mid-1950's and continues in a definable path to today.
Music Accessible To the Widest Audience
Since the mid-1950's pop music has usually been identified as the music and the musical styles that are accessible to the widest audience. This means the music that sells the most copies, draws the largest concert audiences, and is played most often on the radio. After Bill Haley's "Rock Around the Clock" hit #1 on music charts in 1955 the most popular music became the records influenced by rock 'n roll instead of the songs and light standards that had dominated TV's Your Hit Parade weekly countdown show. Since 1955 the music that appeals to the widest audience, or pop music, has been dominated by sounds that are still rooted in basic elements of rock 'n roll.
Pop Music and Song Structure
One of the most consistent elements of pop music since the 1950's is the pop song. Pop music is not usually written, performed and recorded as a symphony, suite, or concerto. The basic form for pop music is the song and usually a song consisting of verse and repeated chorus. Most often the songs are between 2 1/2 minutes and 5 1/2 minutes in length. There have been notable exceptions. The Beatles' "Hey Jude" was an epic 7 minutes in length. However, in many cases, if the song is abnormally long, an edited version is released for radio airplay such as in the case of Don McLean's "American Pie." It was edited down from its original 8 1/2 minutes length to just over 4 minutes for radio airplay. On the other end of the spectrum, in the late 1950's and early 1960's some hit songs clocked in under 2 minutes in length.
The Pop Music Melting Pot
Like other art forms that aim to attract a mass audience (movies, television, Broadway shows), pop music has been and continues to be a melting pot that borrows and assimilates elements and ideas from a wide range of musical styles. Rock, r&b, country, disco, punk, and hip hop are all specific genres of music that have influenced and been incorporated into pop music in various ways over the past 5 decades. Most recently, Latin music seems to be impacting pop music more significantly than at any point in the past.
Pure Pop and Power Pop
Although pop music continues to be a melting pot of styles, there is a genre of pop music that claims to be pop music in its purest form. This music, usually called pure pop or power pop, typically consists of relatively brief (not over 3 1/2 minutes) songs played on the standard electric guitar, bass and drums with vocals that have a very strong catchy chorus, or hook. Art is not a concern. Audience pleasure in listening to the song is the primary goal.
Among the top pure pop or power pop performers of the past are the Raspberries, Cheap Trick and the Memphis group Big Star. The Knack's #1 smash hit "My Sharona" is often considered the biggest power pop chart hit. In recent years groups like Jimmy Eat World, Fountains of Wayne, and Weezer have been seen as successors to classic power pop.