»melisma

melisma comes from the Greek melizein, meaning to sing: melodic, but not mellifluous, comes from this same root (note the double ell in the latter). Melisma means "A group of many notes (usually at least five or six) sung melodically to a single syllable. Melismas are found especially in liturgical chant."
I saw this word in the caption to Sasha Frere-Jones's current essay in The New Yorker. Alas, the online edition lacks the stunning photograph of Mariah on a Vespa, with the caption: Carey established R.& B. as the sound of pop and made melisma a requirement on "American Idol."

Frankly, other than her airbrushed smile, the only thing I know about Ms Carey is that she shares an (impressive!) vocal range with Frank Zappa.

... when she sang her perky dance hit “Emotions” at the 1991 MTV Video Music Awards, she reportedly sounded a G-sharp three and a half octaves above middle C, one of the highest notes produced by a human voice in the history of recorded music. (Party poopers say that the note was actually an F-sharp.)
Carey’s freakish vocal ability explains part of her appeal. In the same way that people went to a San Francisco Giants game in order to see Barry Bonds hit a home run, people buy Carey’s records in order to hear her do things with her voice that no one else can do.
... Carey can sing lower notes, like an alto, and extremely high notes, like a coloratura soprano, which says something about her range but little about her style.