A shaft in an ICE that actuates components that open valves into the combustion chamber to allow the flow of necessary gasses in order for a combustion process to function.
The image below depicts an exhaust and an intake camshaft for a DOHC ICE
In the image below that camshafts can be see at the top of the engine.
This image is of a 4 cycle DOHC (Dual Overhead Cam) design.
An Image of a cam lobe, a component of the camshaft