A rotary laser level is a tool used in construction and surveying to create a precise horizontal or vertical reference line. It projects a rotating laser beam that can be seen over long distances, making it ideal for leveling and aligning tasks. This tool is especially useful for tasks like grading, framing, and installing cabinets. The device typically consists of a laser unit and a receiver. The laser unit spins the beam 360 degrees, while the receiver detects the beam's position. This allows users to easily determine elevation changes across large areas, ensuring accuracy in various projects.