On a violin, guitar, or other stringed instrument, the fingerboard is the long, smooth strip under the strings. You press a string down onto it with your fingers to change the note. On a guitar it usually has metal frets, and players often call that a fretboard; fingerboard still covers it. On a violin there are no frets, and fingerboard is the usual word. Though actually, the rest of the sentence is what tells you it is music talk: it is a workshop word for that strip of wood, not a board you rest your hands on, and not a keyboard.