Bbm6 is Bb, Db, F and G — Bbm with a major sixth added on top.
It sounds bittersweet — minor underneath, major on top. The major sixth over a minor triad comes from the melodic minor, and it is the classic jazz minor tonic.
Minor tonic — an ending chord in a minor key.

| Bb | Db | F | G |
|---|---|---|---|
| 1 | ♭3 | 5 | 6 |
Also written Bbmin6, Bb-6 or Bb minor 6. The same chord either way; which spelling you meet depends on who wrote the chart.
Bbm6 in 2nd inversion puts F in the bass instead of Bb, the 5th of the chord. The notes are the same; what changes is what the bass line does, which is most of why you would reach for it — it lets the lowest voice move by step where the root would have jumped.
2 of Bbm6’s 9 common shapes do this:xx3323x-x-15-15-14-15
Play Bbm6 as a shell — root, third and seventh — and the spare string takes the 9 (C) or the 11 (Eb).
All 9 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 Bbm6 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 Bbm6 belongs to F minor (the iv, the subdominant) and Ab major (the ii, the supertonic).
Every note of Bbm6 is in Bb dorian, Bb melodic minor and Bb half-whole diminished.
Change one note of Bbm6 and you have Bbm (drop the sixth), Bbdim7 (the fifth becomes the flat fifth), Bbm69 (add the ninth), Bbm7 (the sixth becomes the flat seventh), BbmMaj7 (the sixth becomes the major seventh) or Bbmadd9 (the sixth becomes the ninth).
Bbm6 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.