The B flat minor eleventh chord is a 6-note chord consisting of the notes Bb, Db, F, Ab, C and Eb.
You can see these notes highlighted in the interactive piano chart below.
The chord itself is often abbreviated as Bbm11.
Interactive piano diagram for the B flat minor eleventh chord
Chords that are a subset of Bbm11. These contain less notes but all of them are included in Bbm11.