Ornamentation (music)
An Appoggiatura literally means a “leaning note”.  The word comes from the Italian word appoggiare, "to lean upon".  It is a note which wants to fall down to the next one which is part of the harmony.   Composers often wrote an appoggiatura in small print.  This usually means it must be played by taking half the time value of the next note (for example: an appoggiatura in front of a quaver (eighth note) turns both notes into two semiquavers (sixteenth notes).  During the 18th century composers stopped writing them in small print and just wrote them as normal notes.