overhead projector 
noun
A device that projects an enlarged image of an acetate or other transparency placed on it on to a wall or screen by means of an overhead mirror.For many years, overhead projectors lit up transparencies, and slide projectors showed high-resolution 35 mm slides....
- Some of the best ideas were then enlarged, transferred onto the wall with an overhead projector and painted in acrylic paint.
- First, the student uses an overhead projector to project his or her image onto a large piece of stiff paper.