What is it that you put oil on a person who has been chosen?

Oil is commonly used in The Bible to "anoint" those whom God has ordained. I think the Word you are looking for is "anoint." In the Old Testament this was used most often for kings, high priests, and prophets. They used a specific type of oil mixture that can be found in Exodus. After Christ, many others who were not kings, high priests, or prophets were anointed . Now because of Christ anyone who has been reborn and therefore considered a son or a daughter of God can be anointed with oil, or any other liquid for that matter.