A diminished chord is a triad characterized by a root, a minor third, and a diminished fifth. This means the interval between the root and the third is three semitones, and the interval between the root and the fifth is six semitones. For instance, a C diminished chord consists of the notes C, Eb, and Gb.
The distinctive, dissonant sound of diminished chords makes them useful for creating tension and harmonic color. Throughout music history, composers have employed them to add dramatic effect, to create a sense of unease, or to facilitate smooth modulations between keys. Their instability compels the ear to anticipate resolution, making them a valuable tool in musical composition.