Okay kiddo, so you know how there are some songs that have really mean and violent lyrics? Well, sometimes those songs can talk about hurting or killing other people, and that's not okay. That's what we call "murder music".
Some people don't like these songs because they think it's not right to promote violence and hurting others. They even have a movement called "stop murder music" which aims to boycott these kinds of songs and not give them any attention.
It's kind of like when we choose not to play with someone who's being mean or bullies us. We don't want to support or encourage bad behavior. And that's what stop murder music wants to do - to discourage songs that promote violence and instead, promote positivity and kindness in music.