What is the difference between overhead cam and overhead valve?

Overhead valves open vertically from the head into the combustion chamber. Overhead valve engines use a system of lifters, push rods, and rocker arms to operate the valves. The cam on an overhead valve system is adjacent to the crankshaft, and the lifters, push rods and rockers work together to operate the valves.

Overhead cam engines position the camshaft directly above the valves. In that position, there is much less weight of the valve operation mechanism, resulting in a potentially higher engine operating speed.