It is a green cloth, sheet, or board that you have behind you while you play. We use a "Chroma Key" while we stream to delete the background behind you and insert an image of your character behind you on the stream. It looks really nice and is more private because nothing in the room you're in will show. A Green Screen is required to do this... These are very inexpensive and you can buy them online (ebay, amazon, etc) You will not need to buy one to apply, but if you are Selected to be one of the 4 Players for the game it will be a requirement! Here is an example of what it will look like behind you (we have a professional artist that will draw your character for the stream) The video of your face will be laid on top of your characters image.