Protest music is like when you hear someone singing a song, and the song is trying to tell people that something is wrong, and it needs to be changed. You know how sometimes when you're upset at something, you might write a letter or draw a picture to show how you feel? Well, sometimes people who can sing or play instruments use music to show how they feel about things they don't like in society.
For example, sometimes people sing songs that talk about war because they don't like fighting and they want everyone to be peaceful. Or they might sing songs that talk about how unfair it is that some people have more money or power than others.
Protest music tries to make people think about what's going on in the world and encourages them to try and change things for the better. Even though some people might not like hearing these songs because they don't agree with what the singer is saying, it's important for people to be able to express their opinions. That's why protest music exists.