OHC means overhead cam. The cam is above the cylinder head. SOHC engines have a single cam over the cylinder head. DOHC engines have two cams above the cylinder head. All OHC, SOHC, and DOHC engines are also OHV.
It is a type of valvetrain configuration in which the camshaft of the engine is in its cylinder head. When the camshaft is located close to the valves, the engine runs at higher rpm. In a single-overhead-cam (SOHC) layout, one camshaft activates all the valves in a cylinder head while in a double-overhead-camshaft (DOHC) layout, one camshaft actuates the intake valves, and the other operates the exhaust valves.
A camshaft used for operating both valves and unit injectors, located on top of or within the cylinder head. Such camshafts are driven by a multi-gear geartrain off the crankshaft. They simplify the design of the cylinder head and eliminate pushrods, allowing for much larger, open intake and exhaust ports and better breathing.