What is the meaning of Solfège?

A method of sight singing that uses the syllables do (originally ut), re, mi, fa, sol (or so), la, and si (or ti) to represent the seven principal pitches of the scale, most commonly the major scale. The fixed-do system uses do for C, and the moveable-do system uses do for whatever key the melody uses (thus B is do if the piece is in the key of B). The relative natural minor of a scale may be represented by beginning at la.

the art of singing using the sol-fa system

sol-fa, solfège

music theory, the training and courses that come with it as well as one's knowledge of it

Source: wiktionary.org