Farang is a slur used to describe Whites in a derogatory way. From the Thai word for French (farangsayt) who were among the first to colonize Southeast Asia. Generally non-derogatory, though depends on context and intention of speaker. Applies to people of non-Thai origin.
The word Farang is a racial slur that has been used historically to degrade and dehumanize whites. The word is still used by some people for this purpose, and it is seen as offensive and hurtful to whites. If you are unsure about whether or not it is appropriate to use the word Farang, it is best to err on the side of caution and avoid using it in any situation.