Freebase(0.00 / 0 votes)Rate this definition: Keg. A keg is a small barrel. Traditionally, a wooden keg is made by a cooper used to transport items such as nails, gunpowder, and a variety of liquids. More recently, a keg is often constructed of aluminum or steel. It is commonly used to store, transport, and serve beer. Other alcoholic or non-alcoholic drinks, carbonated or non-carbonated, may be housed in a keg as well.