A chord is three or more notes played together. The four basic triads (3-note chords) are built by stacking intervals of thirds.
Major
[0, 4, 7]
Minor
[0, 3, 7]
Diminished
[0, 3, 6]
Augmented
[0, 4, 8]
C Major
Notes: C – E – G
Triad Formulas