Use the noun redundancy to refer to something that's needlessly repeated. As much as you hate the redundancy of math drills, you have to admit that repetition is how you learned to multiply in the first place.
The noun redundancy can also refer to something that is unneeded, or extra. If you own a circus and you want to keep costs down by eliminating redundancy, you may decide you only need two clowns, rather than the whole carload of clowns you planned on. Redundancy comes from the Latin word redundare, meaning to surge, or literally to overflow.