Is this a "slash" chord?


…and what do the 2 slashes (front and back) mean? I originally understood the first one to mean the bass note that is not the root note of a chord?

The C is bass note C. The one on front seems to be telling you it’s either G#Maj9 or AbMaj9 depending on what scale you are in (flat or sharp).
Scaler has done that a few times for me.

Oh, now that you say it, I see it too - it’s alternate naming for the same note, depending on scale - duuh… G# is (“enharmonic equivalent”?) Ab - did I get this right?

Yep, that’s right. I get that sometimes in Scaler if I write the chord in myself or change the voicing of a chord.