Used to warm or cook food, a chafing dish consists of a (usually metal) container with a heat source directly beneath it. The heat can be provided by a candle, electricity or solid fuel (such as Sterno). There's often a larger dish that is used as a water basin into which the dish containing the food is placed to prevent food from burning.
A vessel to hold burning fuel, for heating anything placed upon it.
One dish or vessel within another, the outer vessel being filled with hot water and in direct contact with a heat source, and the inner container to hold the food.