K-pop is not a genre of music. It’s simply popular music from Korea.
The term itself was coined by Koreans because people were classifying Korean music as J-pop in online spaces (such as iTunes), and Koreans were, understandably, upset. Koreans use the term K-pop pretty loosely. It’s most often a synonym for daejung gayo. But because it is a term that is conscious of the international eye, some people use it in a way that is closer to how I use the term “idol pop.”
What is not K-pop? Music that no one is listening to. What is not idol pop? Music that is not made under the idol business model. Therefore, Jay Park from 2PM was an idol but is not an idol now. Whether his music is popular or not, it’s not idol pop. Hyori is getting older; she has a self-driven career and does not circulate as a commodity as idols do, so I wouldn’t call her recent music idol pop. That doesn’t mean it’s not highly popular and successful, though.