Added Tone Chords

Added tone chords are triads with an added note a second, fourth, sixth, ninth, eleventh, or thirteenth above the chord root. For example, if we have a C-Major chord, with the notes C, E, and G, and then add a D on top of the chord, we get a Cadd9 chord. 

Cadd9 chord

The following shows some more examples of added tone chords.

Added tone chords
Added tone chords