What's a Camshaft in an engine?

the controlling device of the opining and the closing of the valves of the intake and the exhaust of the cylinder head.

Cam shaft carries cam profiles (equal to the number of valves) designed to operate cylinder valves in timely manner. The timing of cam shaft is very critical with timing of crank shaft.

I agree with you'r answer Mr. Alex ............ Thanks

Camshaft is the rotary part of a engine used to operate valves,Fuel injection pump,feed pump,lube pump and etc ,Directly coupled with crankshaft by gear drive or chain drive

Also ... I agree with you Mr. Alex

THE CAM IN A BOLCK VALVTRAIN LAYOUT OF PISTON ENGINE IS ONE  WHERE THE CAMESHAFT IS PLACED WITHIN THE CYLINDER BOLCKI.USUALLY BESIDE AND SLIGHTY ABOVE THE CRANKSHAFT ENGINE OR DIRECTLY ABOVE THE CRANKSHAFT IN THE V OF A V ENGINE.

Mr. Yazouri has posted very descriptive article about this subject ... no need to add a comment  

I agree with Mr. Alex answer.

A camshaft is a shaft to which a cam is fastened or of which a cam forms an integral part

It is a solid shaft, with a number of "machined lobes"  normally mounted in the Cylinder block, or more recently on the Cylinder Head to open and close the Inlet and Exhaust valves at the correct time and duration.  It is timed (mechanically) to work at half the Crankshaft speed and, the number of lobes is matched to the number of cylinders in the engine 

Double overhead cams control the opening and closing of a cylinder's valves. Valve timing gears on a Ford Taunus four-cylinder engine — the small gear is on the crankshaft, the larger gear is on the camshaft. The gear ratio causes the camshaft to run at half the RPM of the crankshaft.