Indo is a slur used to describe Indonesians in a derogatory way. Self Explanatory
The word Indo is a racial slur that has been used historically to degrade and dehumanize indonesians. The word is still used by some people for this purpose, and it is seen as offensive and hurtful to indonesians. If you are unsure about whether or not it is appropriate to use the word Indo, it is best to err on the side of caution and avoid using it in any situation.