The term "zip lock" refers to a type of plastic bag with an opening at one end that is sealed shut by a metal or plastic zipper. The name comes from the fact that once the zipper is closed, it creates an air-tight and watertight seal, preventing anything inside from escaping or leaking out. Zip locks are commonly used for storing items in a waterproof and secure manner, such as clothing, documents, or other valuables. They can also be used to create reusable food storage bags by filling them with air and then sealing the zipper shut.