Do is the root of a key in movable Do solfeggio. In the most natural key, C, Do would be C. Basically, solfeggio is relative, not absolute. Most instrumental pedagogy use absolute pitches in North America. Vocal pedagogy has more use of relative pitches. This makes sense, as many instruments have absolute means of playing most notes. The voice does not.
Do is the root of a key in movable Do solfeggio. In the most natural key, C, Do would be C. Basically, solfeggio is relative, not absolute. Most instrumental pedagogy use absolute pitches in North America. Vocal pedagogy has more use of relative pitches. This makes sense, as many instruments have absolute means of playing most notes. The voice does not.
https://en.wikipedia.org/wiki/Solfège?wprov=sfla1
Edit: Don’t ask me why A isn’t the root of the most neutral key. No idea why it’s C.