Imagine you are watching a play and in the background, you see a group of people wearing matching clothes and they all say the same things together. These people are called the "Greek chorus".
The Greek chorus is a group of actors who sing and dance together while also commenting on the main story of the play. Their job is to help the audience understand what is going on, explain how the characters are feeling, and offer advice or warnings.
Think of them like a group of friends who talk about what is happening in a movie or show and try to make sense of it all for you. They are there to help you understand the story better and feel more connected to the characters.
In ancient Greece, plays would often include a Greek chorus to help the audience make sense of the story and to provide more entertainment. Although we don't see them as much in modern plays and movies, they still exist and serve the same purpose when they appear.