Bb11 chord

The B-flat dominant eleventh chord (abbreviated Bb11 chord) is a six-note chord consisting of the notes B♭, D, F, A♭, C, and E♭. The chord is formed by adding an eleventh to the B-flat dominant ninth chord.

In practice, the third (D) and fifth (F) are often omitted from the Bb11 chord to avoid a very dissonant sound, and because it's not always possible to play all notes simultaneously.