The term "fiddle" has several meanings, depending on its context.
1) In a general sense, it can refer to any musical instrument that is played with a bow or by plucking its strings, such as a violin, viola, cello, etc.
2) It can also be used metaphorically to mean "to tamper" or "to meddle," as in the phrase "don't try to fiddle with something that isn't broken."
3) In some regions of North America, particularly Canada and the United States, it is a term for a type of small, sweet citrus fruit.