Delegitimization is when someone tries to make other people think that something or someone is not good or important. It's like when you tell your friends that you don't want to play with someone because they're not cool or fun. Sometimes people do it to be mean, but other times they might do it because they don't like something or someone and they want other people to agree with them.
Imagine you have a favorite toy that you love playing with. But then someone comes along and says, "That toy is boring and nobody likes it." They might try to convince your other friends that your toy is not good, and soon everyone starts to believe them. This is delegitimization because they're trying to make your toy seem less important or valuable than it really is.
Delegitimization can also happen with people or ideas. It's like if you have a friend who always says smart things in class, but then someone else says, "He's not really that smart. He just memorizes everything." They might try to make everyone think that your friend is not as smart as he seems, even though he really is. This is also delegitimization.
Sometimes it's hard to know who or what to believe when people try to delegitimize something or someone. The important thing is to think for yourself and make your own decisions based on what you know is true. Just like you know that your toy is fun to play with and your friend is smart, you should believe in things that you know are good and important, even if other people say they're not.