A resource is anything that can be used for some purpose, but particularly something that is scarce or might become scarce. It differs from a source in that the latter is a place or person from which something useful or valuable can be obtained.
A natural resource is something that exists naturally (i.e., not created by humans) and can be used by humans or other organisms. Such resources can be classified into perpetually renewable, intermediately renewable and non-renewable.
Categories of natural resources include water, air, soil, plants, animals, minerals and fossil fuels as well as specific types of these. Examples of natural resources that are scarce, at least in some locations, and are becoming increasingly so, include fresh water, clean air, soil, helium, cobalt, trees, bees, and petroleum.
The field of economics is the study of the allocation of (i.e., how to best use) scarce resources. Also referred to by economists as factors of production, resources are the inputs used to produce goods and services.