Definition and background:
Decorative notes of short duration added to compositions to emphasize certain notes and to add flavor to the composition. Ornamentation has been used through all periods of music in Western tradition, but are particularly prominent in the late Renaissance, Baroque, and Classical eras. Ornamentation is not limited to specific instruments, but may be performed on almost any instrument, including the voice.See also ornament; embellishment. an elaboration of a given melody. Ornaments could be written out or improvised.
For more information on the music term "Ornamentation" check out these other resources:
Wikipedia - Glossary of Musical Terminology
Virginia Tech Multimedia Music Dictionary
ORB -- Medieval Music Glossary