Guitar skills: 'Add’ chords come in the form of either ‘add9’ or ‘add11’. The name tells you to add either a 9th or 11th interval to a basic major or minor chord. So, Cadd9 is a C chord ...

This add11 only just qualifies as a chord because it is very sparse. From low to high, we have root (A), another root an octave above, 3rd (C#) and the added 11th/4th a semitone above (D).