Agarwood

Pieces of Aquilaria wood lacking the dense and dark resinous agarwood caused by infection

Agarwood or oodh (or just agar) is a dark resinous heartwood that forms in Aquilaria and Gyrinops, trees (large evergreens native to southeast Asia) when they become infected with a type of mold. Prior to infection, the heartwood is relatively light and pale coloured, however as the infection progresses, the tree produces a dark aromatic resin in response to the attack, which results in a very dense, dark, resin embedded heartwood. The resin embedded wood is commonly called gaharu, jinko, aloeswood, agarwood, or oud (not to be confused with 'Bakhoor') and is valued in many cultures for its distinctive fragrance, and thus is used for incense and perfumes.

MORE INFO in wikipedia

and Tajul Bakshi from India