Backer board is a type of building material commonly used in construction and renovation projects, particularly in areas exposed to moisture, such as bathrooms and kitchens. It serves as a stable, water-resistant surface for tile installations, providing support and preventing damage to underlying structures. Typically made from materials like cement or fiberglass, backer board is installed beneath tiles to enhance durability and reduce the risk of mold and mildew. It is often used in conjunction with other materials, such as tile and thin-set mortar, to create a long-lasting and waterproof surface.