Native to Borneo through Indonesia, this leaf is used in cooking only in that region - but in Indonesia in particular it is used a lot. Fresh leaves are used in curries and with meat, and dried leaves when fresh are not available. Packages of dried leaves are often labeled "Indian Bay Leaf", an obsolete usage from when Indonesia was called East India.
Many cookbooks, presuming you can't get Daun Salam, suggest using European bay leaves. This is bad advice - Salam is not at all related to either European or Indian bay leaves, both of which are highly aromatic Laurels with an entirely different and more powerful flavor. Daun Salam is a myrtle. The leaves are thinner and less aromatic, more earthy, and with a definite hint of citrus. A much better substitute is Curry Leaf (which is a citrus). Certainly not exact, but at least in the ballpark. Otherwise, leave it out
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