A bottle cap is a small, typically circular cover that seals the opening of a bottle. It is designed to keep the contents inside fresh and prevent spills. Bottle caps can be made from various materials, including plastic and metal, and often feature a threaded or snap-on design for easy application and removal. Bottle caps are commonly used on beverage containers, such as soda bottles and water bottles. They may also include features like tamper-evident seals to ensure safety. Some bottle caps are designed for specific purposes, such as child-resistant caps for medications, enhancing both convenience and security.