If you reintroduce something, you start using it again, or you bring it back to a place, after it has not been used there, or has not lived there, for some time. A government might reintroduce a tax it had dropped. A school might reintroduce uniforms after years without them. People who work with wild animals reintroduce birds, fish, or deer to a forest or a river where those animals used to live and then disappeared. Though actually, the word is not bring it back for five minutes. The feeling is: it was gone for a real stretch of time, and now someone is putting it back on purpose. You will hear it in news about nature, money, and old rules. A lighter everyday use is to reintroduce two people who have already met — that is just introduce again in a room, and it is not the heavier sense this entry is for.