INSTRUMENT COMMON
A fiddle is a bowed string musical instrument, most often a violin. It is a colloquial term for the violin, used by players in all genres, including classical music.
If you have proficiency with a given musical instrument, you can add your proficiency bonus to any ability checks you make to play music with the instrument. A bard can use a musical instrument as a spellcasting focus. Each type of musical instrument requires a separate proficiency.