Neumes
The term, Melisma, refers to the singing of a single syllable of text while moving between several different notes in succession. In melismatic chants, a syllable may be sung to a large number of notes, a series of smaller such groups of neumes are written in succession, read from left to right. Music sung in this style is referred to as melismatic, as opposed to syllabic, in which each syllable of text is matched to a single note.
Sources:
“Neume” in “Medieval Music Glossary” of The ORB [Online Reference Book for Medieval Studies] Encyclopedia.
“Notation” in database: Grove music Online.