Pop is a catch-all term that's taken on myriad meanings over the years. In its nascent days, "pop" applied to commercially successful artists who won broad public interest with lighthearted fare. As the 20th century progressed, the notion of popular music also began to indicate a particular sound of pure aural amusement: three minutes of bright melodies and infectious hooks. Today, pop music continues to swerve back and forth between these two aspects of its definition. Because the term essentially refers to music composed for popular appeal, the aesthetics of pop vary almost constantly according to the tastes of the time: doo-wop, disco and electronic dance music have all been pop, as have 50 Cent, Patsy Cline and Nirvana. At the same time, artists in very un-mainstream genres (like indie rock and electronic music) often play or at least play with that quintessential pop style of bright melodies and infectious hooks. This is the place for the music that people have heard on the radio and blasted out car windows across the decades -- music from Justin Timberlake to Rihanna, Diana Ross to Bee Gees, Rufus Wainwright to Selena.