Basically it was a product of infection, there are 30 species of oud or agarwood producing species in the world. And 16 out of that are in Indonesia, so I am in the center of world’s oud producing country. So let’s continue, when the oud or agarwood producing trees are under attack by microbes, be it be fungus, or other micro organism or exposed to forest fire or scratched by animals, struck by lightning, broken when other trees fell on agarwood producing trees and other cause such as ant or termite attack the trees activated defence mechanism to stop the attacker and block it’s activity. After years of infections eventually it will be oud or agarwood.
There are many names for agarwood, in Bahasa Indonesia and Bahasa Melayu it was called as “Gaharu”, it was believed from Sanskrit word “aguru” which literally means the heavy wood, because if agarwood if it was infected after years it will eventually sink due resin deposit. Other naming such Oud or other spelling Aoud (عود) is an Arabic word which also means wood, The Japanese called is Jinkou
(沈香) which means the sinking perfume this is also refer to previous explanation that very high grade oud is sink. The Chinese also have name Chen Xiang which also a synonims to the Japanese word. There are many other names in local language kayu alim, Engkaras, Las, Age and so on.