Oudh/Oud is an oil that is derived from a tropical tree called Agar or Aquilaria. In common language, the wood it is derived from is called Agarwood. The family of agar trees has about 15 different species. That makes the scent derived from each of them different.
The tree is believed to have origins in the Asian Subcontinent. Specifically, it is found in Assam region of India. From Assam, the trees have spread out to Bangladesh and much of South East Asia.
A fascinating fact about the Agar tree is that, even upon burning its trunk or any wood chip, a great pleasing scent is obtained. This is why Oudh chips are used to scent religious places of worship. In many religions, Oudh perfume has taken place in religious festivities and occasions.
Buring of Oudh/Oud in the morning in the Middle East is a common sight. The Arabs love the aroma it produces and have made the burning and wearing of oudh a must-have morning ritual. People in China and Japan also are in love with Oudh Perfumes.