In a chord diagram, the highlighted part that represents the furthest to the right and is above the diagram typically indicates a chord symbol. The chord symbol shows the name of the chord being played.
The other options relate to different aspects of guitar playing:
- An open string would not typically be highlighted above the diagram.
- The nut is usually represented at the top of the diagram, but not as a highlighted area.
- A left-hand finger might be indicated by numbers on the diagram, showing which fingers to use on which frets, but again, wouldn't be the highlighted part above the diagram.
So, the correct answer is a chord symbol.