It used to be that popular music or "pop," as it came to be known, encompassed every type of music with the exception of classical music. I think even now the same rule applies. Country, R&B, Jazz and Latin are all forms of popular music.
The term though now is applied more to music that teenagers and young adults like. Justin Bieber would be considered pop, but you wouldn't put an artist like Jack White or a group like Coldplay in the same category, even though they might show up on the pop charts. These artists would be classified as rock artists.
The line is very vague as to what distinguishes pop from rock. That is the trouble with musical categories.
Duke Ellington once said something to the effect that there should only be two categories of music, good music and bad music. I wholeheartedly agree.