A cylinder head is a component in an internal combustion engine that sits on top of each cylinder. It serves as the cap to the cylinder and has several functions, including containing the cylinder, providing a seal between the cylinder and the rest of the engine, guiding the flow of air and fuel into the cylinder, and allowing for the escape of combustion gases from the cylinder. The head also contains ports for the intake and exhaust valves to open and close as needed during the four-stroke cycle of an internal combustion engine.