n. A passage of several notes sung to one syllable of text, as in Gregorian chant.
the GNU version of the Collaborative International Dictionary of English
n. A piece of melody; a song or tune, -- as opposed to recitative or musical declamation.
n. A grace or embellishment.
The Century Dictionary and Cyclopedia
n. In music: A song, melody, or air, as contrasted with a recitative or declamatory passage.
n. A melodic decoration, grace, fioritura, or roulade.
n. A cadenza.
Word Usage
"It's called melisma, and most of the contestants on this overblown karaoke-thon simply can't resist contorting their high notes into some pseudo-gospel, neck-vein popping vocal run that's supposed to make everybody in the studio audience shit their pants out of sheer wonder."