There are only a limited amount of resources on the planet; these can be described as scarce or finite resources, for example, oil, coal, trees.
These scarce resources are called economic goods. Not all resources are scarce, these are called free goods, for example, salt water.
In reality nearly all goods are economic goods; clean air was often quoted a free good as it could be used without worrying about scarcity. Increased pollution has led to many economists questioning whether air is in fact a free good.