Melisma is the singing of several notes to one syllable of text. For example, in the Christmas carol ‘Ding Dong Merrily on High’, there is a melisma of 31 notes to the ‘o’ of “Gloria”!
Melisma is used in many musical genres and cultures, such as in plainsong (Western Church chants), Fado (a type of Portuguese singing) and modern pop music.