What is it called when you are painting a room and project on image onto the wall so you can paint the outline or shadow so there is a subtle outline of the scene or image?

The technique you're referring to is commonly known as "projected painting" or "image projection." Artists use a projector to cast an image onto a wall, allowing them to trace the outlines and details accurately. This method helps create a subtle, guided framework for painting, ensuring precise proportions and placement of elements in the scene.