The original application of the term is to music of the 1880s Tin Pan Alley period in the United States. Although popular music sometimes is known as "pop music", the two terms are not interchangeable. Popular music is a generic term for a wide variety of genres of music that appeal to the tastes of a large segment of the population, whereas pop music usually refers to a specific musical genre within popular music. Popular music songs and pieces typically have easily singable melodies. The song structure of popular music commonly involves repetition of sections, with the verse and chorus or refrain repeating throughout the song and the bridge providing a contrasting and transitional section within a piece.
In the 2000s, with songs and pieces available as digital sound files, it has become easier for music to spread from one country or region to another. Some popular music forms have become global, while others have a wide appeal within the culture of their origin. Through the mixture of musical genres, new popular music forms are created to reflect the ideals of a global culture. The examples of Africa, Indonesia, and the Middle East show how Western pop music styles can blend with local musical traditions to create new hybrid styles.
Scholars have classified music as "popular" based on various factors, including whether a song or piece becomes known to listeners mainly from hearing the music (in contrast with classical music, in which many musicians learn pieces from sheet music); its appeal to diverse listeners, its treatment as a marketplace commodity in a capitalist context, and other factors. Sales of 'recordings' or sheet music are one measure. Middleton and Manuel note that this definition has problems because multiple listens or plays of the same song or piece are not counted. Evaluating appeal based on size of audience (mass appeal) or whether audience is of a certain social class is another way to define popular music, but this, too, has problems in that social categories of people cannot be applied accurately to musical styles. Manuel states that one criticism of popular music is that it is produced by large media conglomerates and passively consumed by the public, who merely buy or reject what music is being produced. He claims that the listeners in the scenario would not have been able to make the choice of their favorite music, which negates the previous conception of popular music. Moreover, "understandings of popular music have changed with time". Middleton argues that if research were to be done on the field of popular music, there would be a level of stability within societies to characterize historical periods, distribution of music, and the patterns of influence and continuity within the popular styles of music.
Anahid Kassabian separated popular music into four categories; "popular as populist," or having overtones of liberation and expression; "popular as folk," or stating that the music is written by the people, for themselves; "popular as counterculture," or empowering citizens to act against the oppression they face; and "popular as mass," or the music becomes the tool for oppression. A society's popular music reflects the ideals that are prevalent at the time it is performed or published. David Riesman states that the youth audiences of popular music fit into either a majority group or a subculture. The majority group listens to the commercially produced styles while the subcultures find a minority style to transmit their own values. This allows youth to choose what music they identify with, which gives them power as consumers to control the market of popular music.
Form in popular music is most often sectional, the most common sections being verse, chorus or refrain, and bridge. Other common forms include thirty-two-bar form, chorus form *(Middleton pg 30), and twelve-bar blues. Popular music songs are rarely composed using different music for each stanza of the lyrics (songs composed in this fashion are said to be "through-composed").