Do you mean the difference between effectiveness and efficiency? If so, effectiveness, or if you describe something as "effective," it means that it is adequate to accomplish a certain purpose, or producing the intended or expected result.
Efficiency, or if you describe something as "efficient," you are saying that it is performing or functioning in the best possible manner with the least waste of time and effort.
Both are similar, but efficiency is effectiveness done in a timely manner, if that makes sense :)