(in indonesia) a person who is not indonesian, especially a white person. The word bule, however, has a more curious origin See examples of bule used in a sentence.
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The key takeaway here is that bule generally points to someone who is clearly not local, usually distinguished by their appearance, such as lighter skin or different hair color.
In its most common usage, especially within indonesian and malay contexts, bule is an informal term used to refer to a foreigner, particularly one who is caucasian or from a western country.