solfège syllable; note name in movable do
In movable do solfège, 階名 refers to the relative note name (do, re, mi, etc.) that changes with the key, as opposed to 音名 (fixed pitch name).
In movable do solfège, the solfège syllables change depending on the key.
Practicing singing with solfège syllables makes it easier to hit the right pitches.
solmization
Compound of 階 (かい, 'scale' or 'step') and 名 (めい, 'name'), literally 'scale name'. The term is used in music theory to distinguish relative note names from fixed pitch names.