Defamation is when someone says or writes something untrue and mean or harmful about another person, and it can hurt that person's feelings or damage their reputation. In a film, defamation is when a character or real person is portrayed in a negative way that is not true or fair, and it can make people think badly of them even if they've done nothing wrong. It's like when someone tells a lie about you to your friends, and then they start thinking you're not a good person. In a film, it can also be someone spreading rumors or saying things that are untrue and harmful about another person or group of people. It's important to always tell the truth and not say mean things about others, even if it's just pretend in a movie.