What do double notes mean piano?
It means that the C is part of the melody and also part of the harmony. If you were arranging this piece for ensemble you have two instruments on the same note.
What does double note mean in music?
In music, a double whole note (American), breve, or double note is lasting two times as long as a whole note (or semibreve). It is the second-longest note value still in use in modern music notation.