What is an appoggiatura?

Question

I need to know this for a music class. Please help.

Answer 1

from Dictionary.com: a note of embellishment preceding another note and taking a portion of its time

from Wikipedia: The acciaccatura (sometimes called short appoggiatura) is perhaps best thought of as a shorter, less melodically significant, variant of the long appoggiatura, where the delay of the principal note is scarcely perceptible - theoretically subtracting no time at all. It is written using a grace note (often a quaver, or eighth note), with an oblique stroke through the stem:

Answer 2

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Leaning note; grace note; note of embellishment usually one step above (sometimes, though seldom, it is one step below) the main note. Before an even or unaltered note, the appoggiatura generally receives its face value, that is one-half the value of the note that follows; before a dotted note it receives more than its face value, that is to say that it should be given two-thirds of the value of the following note. If the note is of the same pitch as the principal note of the appoggiatura, the grace note receives the entire value of its principal note, but is carried to the next note with strong portamento.