Fizz keeper is a term used to describe a cap or stopper that helps keep carbonated drinks from going flat. There are several synonyms for fizz keeper, including bottle cap, soda cap, can lid, airtight seal, pressure cap, and carbonation preserver. These items are typically made from durable materials, such as plastic, metal, or rubber, and are designed to fit securely on the top of bottles or cans of soda, beer, or other carbonated beverages. By preventing air from getting into the container, fizz keepers help preserve the carbonation and keep drinks bubbly for longer periods of time, which is especially useful when enjoying drinks outdoors or at events where drinks might sit for a while before being consumed.