Frankincense is an aromatic gum resin from trees of the genus Boswellia, which grow in Somalia and southern parts of the Arabian peninsula. The ancient world used it for religious and medicinal purposes. Right up to the Middle Ages it was considered an Arabian trading commodity.
These days it is used as an ingredient of incense, perfumes and some fumigants. It is obtained by extracting the milky juice which hardens on exposure to semi-opaque lumps.