Mastic is an aromatic resin produced by the mastic tree (Pistacia lentiscus). The Greek island of Chios has been famous for producing it since ancient times, so much so that it is called the "tears of Chios." Small granules that give your coffee and desserts an unmistakable, distinctive aromatic flavor.
Preferably grind it with a little sugar before adding it to recipes, so it spreads evenly.
Store in an airtight container in a dry place, away from heat and sunlight.