A keg is a cylindrical container used primarily for storing and dispensing beverages, especially beer. Kegs come in various sizes, with the most common being the half-barrel, which holds about 15.5 gallons. They are typically made of stainless steel, which helps preserve the quality of the beverage inside. Kegs are equipped with a tap system that allows for easy pouring. When a keg is tapped, pressurized gas, often carbon dioxide, is used to push the liquid out. This method helps maintain carbonation and freshness, making kegs a popular choice for parties and events.