A rentier state is a country that has a lot of money coming in from investments or from resources like oil or gas that it can sell. The money it gets from these investments and resources is called "rents". The money from the rents can be used to pay for things like schools and roads that the country needs, or it can be saved for later. Rentier states usually have governments that are very rich and powerful, even though the people in the country might not be very wealthy.