Cb11 chord

The C-flat dominant eleventh chord (abbreviated Cb11 chord) is a six-note chord consisting of the notes C♭, E♭, G♭, B♭♭, D♭, and F♭. The chord is formed by adding an eleventh to the C-flat dominant ninth chord.

In practice, the third (E♭) and fifth (G♭) are often omitted from the Cb11 chord to avoid a very dissonant sound, and because it's not always possible to play all notes simultaneously.