Flashing is a type of material used on a roof to prevent water from seeping into areas where the roof meets another surface, such as a chimney, skylight, or vent pipe. Flashing is typically made from thin strips of metal, such as aluminum or copper, although it can also be made from other materials, such as rubber or plastic.

The purpose of flashing is to create a water-resistant barrier between the roof and the other surface. This is important because water can seep into even the smallest gaps or cracks and cause damage to the roof, the other surface, and the interior of the building.

Flashing is installed by placing the material over the joint between the roof and the other surface, and then sealing it with roofing cement or other sealant. Flashing may be installed in several different areas of a roof, depending on the design of the roof and the features of the building.

Overall, flashing is an important component of a roof system that helps to protect the building from water damage and ensure that the roof performs properly over time.