So, kiddo, have you ever heard of someone who did something bad and then their friends or family said, "I don't want to be friends with you anymore because of what you did!"? That's kind of like what the denunciation movement is all about.
Some people in history did really bad things, like hurting or even killing other people. When other people found out about it, they didn't want to be associated with the bad person anymore. They didn't want to be friends or work with them. They wanted to make it clear to everyone that they didn't approve of the bad things the person did. This is called denouncing someone.
In some cases, a whole group of people might band together to denounce one person or a whole group of people. This is called a denunciation movement. It's like saying, "We as a group don't accept this behavior and we won't stand for it."
Denunciation movements can happen for all sorts of reasons. Maybe someone did something very unpopular or against the beliefs of the people around them. Maybe they committed a crime that hurt a lot of people. Whatever the reason, a denunciation movement is a way for people to make it clear that they don't approve of something or someone's actions.