Imagine you're playing with your favorite toy, let's say a puzzle. You put it all together the way you want it, but then you realize you want to change it up a bit. You want to add more pieces or take some away. This is kind of like what a director's cut is for a movie.
The director's cut is a version of a movie where the director has gone back and made some changes. They may have added scenes that were cut from the original movie or changed the order of scenes. They may have also added more dialogue or changed the music.
The reason directors make these changes is because they want to make the movie they always wanted to make. Sometimes the original version of a movie is changed by the studio or producers to fit a certain style, or to make it more appealing to audiences. The director's cut allows the director to have full control and show their vision of the story.
So, just like you can mix up your puzzle and make it the way you want it, directors can make a version of their movie the way they want it, and that's what a director's cut is.