A flange is a type of metal or plastic plate that extends outwards from a pipe, duct, or other structure. It has a broad flat surface on one side and may have bolt holes around its perimeter to secure it in place. Flanges are commonly used for connecting pipes together, attaching them to valves, or joining them with other equipment such as pumps or heat exchangers. They come in various sizes and shapes depending on the application they will be used for.