The world of music has consistently evolved. Genres have been defined and then the classic definitions have been junked to make way for new genres. In music, the concept of genres, subgenres and mixed genres is not new. Fusion has always been integral to music of all forms. If you had country blending with rock at one time then you had the lines blurring between gothic and heavy metal. Pop itself has a very vague description and it is often not regarded as a genre at all by hardcore rock musicians.