Fm chord inversions
Fm/Ab and Fm/C are the first and second inversions of the F minor. This means that the bass tone is shifting from F to Ab or C.
Try in a chord progression
Fm/Ab - Gm/Bb - Eb
Fm - Fm/C - Bbm
When stumble upon these chord names, you can choose to ignore the alternate bass note and play the regular F minor. It will always sound ok, but it may lack some subtle additions to the sound. Notice that the diagram version of Fm/C presented above is similar with the Fm barre shape with the bass note on the fifth string except that the sixth string has been included.
Another option for Fm/Ab is XXX111. Fm/C can be played in first position as X33111.
Theory of the Fm/Ab and Fm/C chords
Both chords consist of the notes F, Ab, C. The difference is that the order of notes shifts. A flat is the bass note in the first inversion and C is the bass note in the second inversion.
Alternative chord names
Fm/Ab is identical with Ab6(no5).
See also Fm7 inversions
Fm x -x - F - Ab - C - F
Fm/Ab x -x - Ab - C - F - Ab
Fm/C C - F - C - F - Ab - C
Guitar versions of the chord
Notes in chordFm F - Ab - C
Fm/Ab Ab - C - F
Fm/C C - F - Ab
Only the order of notes differs