Auxiliary º7 chord
This is a º7 chord that doesn’t have any root movement (unlike ascending º7 or descending º7 chords). It’s simply an alteration of an “existing” chord.
Common progressions:
Iº7 -> I- This is a “delayed resolution”
Iº7 -> I6- Only 2 notes move
V7 -> VIm7/b7 -> Vº7 -> I