A natural resource is what people can use from the natural environment. Examples of natural resources are air, water, wood, oil, wind energy, natural gas, iron, and coal.
The dividing line between natural resources and man-made resources is not clear-cut. Hydro-electric energy is not a natural resource because people use turbines and generators to convert the energy of moving water to electric current. Petroleum and ores are natural, but need work to make them into usable refined oil and metals. Atomic energy comes from metallic nuclear fuel, like fissionable uranium and plutonium, but rocks need technical work to make them into these nuclear fuels.