The term 'overhead projector sheet' refers to a sheet of ACETATE, which is a transparent plastic material. ACETATE is commonly used in overhead projectors because it is lightweight and can be easily manipulated. It is also resistant to heat and chemicals, making it an ideal choice for projecting images onto a screen. The sheet of ACETATE is placed on the projector's surface and then illuminated by the projector's light source. This allows the image to be projected onto the screen.