A triad is a set of three notes or pitch classes that are played simultaneously. In Western classic music it consists of a root, the third, whose interval above the root is a minor third (three semitones) or a major third (four semitones), and a fifth, whose interval above the third is a minor third or a major third. Triads can be classified according to the combination of major and minor thirds they contain into major, minor, augmented and diminished. Some music theorists in recent decades have expanded the use of triad to include any set of three simultaneous notes.