Pop Rock
Pop Rock is the name most commonly given to Popular Music some time after the emergence of Rock and Roll in late '50s, and it was used regularly until sometime in the late 20th or early 21st century, when Rock Music stopped being a major part of popular music. The term is extremely vague and imprecise, literally combining two types of popular music into a new term. But it was necessary, and it was necessary because of the British Invasion.
The British Invasion Invents Pop Rock
Before the British Invasion, popular music in the United States and the world consisted of many different, disparate genres. The United States had the largest popular music industry in the world, by far, so we'll focus there. In the US in the early 1960s the following popular music genres existed:
This is not an exhaustive list, by any means. There was some crosspollination between these genres but not much. And when an artist from one genre played music from another genre, they usually switched their sound to that genre's. For example, Elvis would record gospel songs and records which sounded only like gospel and not like rock and roll. But then the British Invasion happened. The British didn't know about American genre conventions and they didn't know about the segregation of the music industry, be it recording studios and labels, radio stations or concert halls. To the British, all the popular music coming out of the US was the same. So when they sought to reproduce it, they mashed everything together The band that did this most often before anyone else is The Beatles. Their early music smashed the boundaries between American genres and created one gigantic one, Pop Rock. They would show similar disregard when they merged their music with American folk music, to create Folk Rock and when they helped create Psychedelic Music.
