This is a stainless steel round roll-top chafing dish, also known as a food warmer or chafer.
It is used to keep food warm, not to cook it.
Heat is typically provided by a small alcohol or canned fuel burner placed in the holder underneath.
The dish usually consists of a stand, a water pan, a food pan, and a lid.
The roll-top lid design allows the lid to be opened and closed smoothly, often staying in an open position for self-service buffets