Definition from Wiktionary, the free dictionary
- (uncountable) the science or study of rockets and their design
- (uncountable, idiomatic) anything overly complex, detailed or confusing
- It's not rocket science. Just screw in the bulb and flip the switch.
anything overly complex (idiomatic)
Usage notes 
- This phrase is usually used in a negative comparison, as in the example above, to show that something is (or should be) simple, straightforward, or obvious.