https://en.wikipedia.org/wiki/Half-diminished_seventh_chord
WebIn music theory, the half-diminished seventh chord (also known as a half-diminished chord or a minor seventh flat five chord) is a seventh chord composed of a root note, together with a minor third, a diminished fifth, and a minor seventh (1, ♭ 3, ♭ 5, ♭ 7). For example, the half-diminished seventh chord built on C, commonly written as Cm7(♭5), …