not much point on a stock engine.
As Fred said, an engine is controlled by an ecu.
The ecu stores fuel and ignition requirments for a given load/speed event. the best way to describe the data is in a "look-up table", whereby for every load and speed event there is a certain fuel/ign value to make the engine run. this value on a stock ecu however isnt optimum for performance. basically, "remapping" changes the fuelling and ignition variable to increase perfromance.