...music of, and since, the 'TIn Pan alley' era, i.e. the 1880s onwards in the USA and the early years of the 20th century in Europe.  the music that, with the growth of industrialization in the 19th century, began to develop distinctive characteristics in line with the tastes and interests of the expanding urban middle classes.
^popular music. CollinsDictionary.com. Collins English Dictionary - Complete & Unabridged 11th Edition. Retrieved October 01, 2012
^Oxford Dictionaries. " including rock and pop and also soul, reggae, rap, and dance music"