A louver is a ventilation product that allows air to pass through it while keeping out unwanted elements such as water, dirt, and debris. A number of fixed or operable blades mounted in a frame can provide this functionality. ... This gives a comparison of a louvered opening to an unobstructed opening.louver, also spelled Louvre, arrangement of parallel, horizontal blades, slats, laths, slips of glass, wood, or other material designed to regulate airflow or light penetration. Louvers are often used in windows or doors in order to allow air or light in while keeping sunshine or moisture out.