Answer: There one departs the realm of counterpoint and arrives at decoration or ornament. "Double appoggiatura" and "triple appoggiatura" are names for pairs or triplets of grace notes that are played quickly at the time of the primary tone that they precede.

When written as grace notes they will appear as two or three small notes preceding the main note. If written out as they would sound, they will appear as two or three very fast notes followed by the longer note and slurred to it.

Again the key is that the "main" note is the one that is part of the harmony, and these decorations arrive "on the beat," taking time from the main note. Like this: