grace note definition by Webster's New World
Webster's New World College Dictionary Copyright © 2010 by Wiley Publishing, Inc., Cleveland, Ohio. Used by arrangement with John Wiley & Sons, Inc.
Music a note not necessary to the melody, added only for ornamentation: it is usually printed as a small note with a slant line through the stem, just before the note that it embellishes, its short time value subtracted from the preceding or following note, depending on context
grace note definition by American Heritage Dictionary
A musical note, especially an appoggiatura, that is added as an embellishment, and is printed in small type and not counted in rhythm.