Basically it is that あなた can't monetize property that does not belong to あなた / that あなた did not create and when あなた try to claim it as your own original work.
However this 'copyright infringement' deal is very much abused によって content owners that aren't aware of the fair use act (i.e. for educational purposes).
There is a big grey area regarding copyright. Think about artists that create fanart. That there is a huge grey area of copyright. Technically it is the artist's own work, however they are using intellectual property that is not theirs. It's pretty stupid and overly complicated.
Another grey area is AMVs (animated 音楽 videos). That is a huge passion of mine, and despite me putting hours into creating my own idea of a 音楽 video, they often get a copyright infringement stamp on it due to the music, so all money that video now makes goes to the musician. I think that in those cases it should be some sort of percentage スプリット, 分割 in profits. It is unfair that all profits go to the person that did not make the original video, however it is a good idea that profits are スプリット, 分割 to the creator of the music.
This is also why あなた see your favourite youtubers not using 人気 songs in their videos. They use what is called royalty free 音楽 so they don't get a copyright infringement notice.