The document discusses the origins and evolution of the pop rock genre. It notes that pop rock emerged in the late 1950s through the work of artists like Chuck Berry and Elvis Presley who blended rock and roll with pop music styles. In the early 1960s, bands like the Beatles popularized pop rock and influenced other artists such as the Rolling Stones and Jimi Hendrix to incorporate pop elements into their rock music. The document then examines how the band Fall Out Boy's musical style has transitioned over time from emo to a more mainstream pop rock sound, demonstrating how pop rock can serve as a hybrid genre for artists that don't fit neatly into only pop or only rock.