The third voice from the top lowered an octave. The dropped voice becomes the bass, which is why a string is skipped.
Bbm11 is Bb, Db, F, Ab, C and Eb — Bbm9 with the eleventh added on top.
It sounds spacious and slightly unresolved. The eleventh is a whole step above the minor third, so unlike its major counterpart it fits without a fight.
Pre-dominant or minor tonic — it hangs rather than moves.

| Bb | Db | F | Ab | C | Eb |
|---|---|---|---|---|---|
| 1 | ♭3 | 5 | ♭7 | 9 | 11 |
Also written Bbmin11, Bb-11 or Bb minor 11. The same chord either way; which spelling you meet depends on who wrote the chart.
The same operation one voice further down: the third voice from the top falls an octave and becomes the bass.
That leaves a bigger hole under the top three notes, so a string gets skipped: the muted string in the middle is the shape, not a mistake.
Bbm11 has 8 of them, on strings 6-4-3-2 and strings 5-3-2-1, from open position up to the 11th — every inversion the chord has: Bb in the bass, Db in the bass, Ab in the bass and Eb in the bass. The one to learn first is the Ab shape at the nut.
4 of them sit on strings 6-4-3-2, so you can run the inversions up one set without changing strings — which is the whole reason to learn them as a family rather than as separate grips.
Six notes and four fingers, so something has to go. Keep Db and Ab (they fix the quality) and Eb and C (what the symbol is about). Let F and Bb go, in that order — a perfect fifth says nothing the root has not, and in a band the bass has the root.
Play Bbm11 as a shell — root, third and seventh — and the spare string takes the 13 (G).
All 7 common shapes as fret numbers, lowest string first. Hover or tap one to see it drawn.
How you get to it. The turn that lands on Bbm11 is Cm7♭5 to F7♭9: the ii and the V of Bb minor, which is where a minor tonic is usually arrived at rather than simply begun on.
In which keys. Every note of Bbm11 belongs to C# major (the vi, the submediant), F minor (the iv, the subdominant), Ab major (the ii, the supertonic) and Bb minor (the i, the tonic).
Every note of Bbm11 is in Bb dorian and Bb natural minor.
Change one note of Bbm11 and you have Bbm9 (drop the eleventh), BbmMaj11 (the flat seventh becomes the major seventh) or Bb11 (drop the minor third).
Bbm11 is a minor chord — root, minor third, fifth. Minor chords on every root.
The common shapes and the derived voicings come from different places, and both are explained in how this site is built.
Shows each chord the way this style would voice it, and marks which of its alternatives belong to the idiom.