Flashing (weatherproofing) is a product used to provide a weatherproof seal around penetrations in a building's roof or walls. It is typically used around chimneys, pipes, or edges on roofs; interruptions in a wall; or around window or door sills.
Flashing is typically produced as a sheet of aluminum, copper, steel, or lead, but may also take the form of a flexible rubberized sheet. Additional types include flashing tape, as shown below.
Aluminum flashing; flashing tape.
Image credit: Roslyn Supply | ULINE