Generally, in music, a diminished chord is a chord which has a diminished fifth in it. More specifically, it is a three-note chord (a diminished triad) consisting of a minor third and diminished fifth above the root - if built on C, a diminished chord would have a C, an E flat and a G flat. The interval between the upper two notes is also a minor third - thus, the chord consists of two minor thirds stacked on top of one another.