Valve gear or valvetrain is the system which opens and closes the valves. Conventionally this is controlled by a camshaft, with motion transferred to the valves by tappets and (sometimes) rockers and pushrods.
Camless valvetrains are now being developed which operate the valves using electro-hydraulic or electro-pneumatic systems.
Choose a letter from the Jargonbuster
Choose from above to see the list of jargon for that letter,
or see the full Jargonbuster list here