The F-flat dominant seventh flat five chord (abbreviated "Fb7(b5) chord") is a four-note chord consisting of the notes F♭, A♭, C♭♭, and E♭♭. The chord is formed by lowering the fifth of a F-flat dominant seventh chord a half step.
F-flat dominant seventh flat five chord
F♭ A♭ C♭♭ E♭♭
1 3 ♭5 ♭7
tetrad (four-note chord)