Roof flashing can refer to the weatherproofing shielding put around objects which protrude from the the protective covering that covers or forms the top of a building (such as pipes and chimneys, or the edges of other roofs) to deflect water away from the seams. Its name likely derives from the fact that metal flashing (typically copper or aluminum) reflects flashes of sunlight. Modern flashing may also be rubber or other waterproof synthetic materials, but metal is still frequently used.
