An overhead projector (OHP) is a device featuring a lightbox, mirror, and lens system that allows users to project images or data onto a screen or wall. It works with transparent acetate sheets printed or written with information, making it possible to display text, diagrams, or photographs to a group audience.
OHPs were widely used in classrooms, business presentations, and workshops before the advent of digital projectors. They remain a useful tool for hands-on demonstrations or situations where simple, reliable projection of visual information is required without complex technology.