Final answer:
The flashing around a plumbing vent pipe is known as a roof jack, which is used to prevent water from seeping into the building around the vent pipe.
Step-by-step explanation:
The flashing around a plumbing vent pipe is called a roof jack. A roof jack is a type of flashing specifically designed to seal around the penetration where a plumbing vent exits through a roof. It helps prevent water from seeping into the building around the vent pipe. Roof jacks are typically made from materials like rubber, metal, or a combination of both, and they conform to the shape and size of the vent pipe to create a tight, weatherproof seal.