Fb11 chord

The F-flat dominant eleventh chord (abbreviated Fb11 chord) is a six-note chord consisting of the notes F♭, A♭, C♭, E♭♭, G♭, and B♭♭. The chord is formed by adding an eleventh to the F-flat dominant ninth chord.

In practice, the third (A♭) and fifth (C♭) are often omitted from the Fb11 chord to avoid a very dissonant sound, and because it's not always possible to play all notes simultaneously.