Oriental is a slur used to describe Asian in a derogatory way. Considered offensive because it dates back to "Orientalism," when Asians were considered savages and Asian women were all seen as sexual objects.
The word Oriental is a racial slur that has been used historically to degrade and dehumanize asian. The word is still used by some people for this purpose, and it is seen as offensive and hurtful to asian. If you are unsure about whether or not it is appropriate to use the word Oriental, it is best to err on the side of caution and avoid using it in any situation.