Scarcity is one of 51 concepts identified by the National Council on Economic Education. Scarcity is an economic problem because one of the main factors that drives economics is the relationship in supply versus demand; if something is in demand and also in short supply, it is more scarce and therefore garners a higher price.
The field of economics looks at how purchasing decisions are made and what factors affect the choice to buy a given item. The principal of scarcity results from having unlimited wants in a world of restricted resources. The theory says that society has a limited means to produce, and therefore fulfill, all the desires and demands placed on a given market.
One simple example is produce shopping in a supermarket. When a fruit or vegetable is at its peak of production there is more of that food available and the price for it is lower than when that same item is purchased off season. When a food isn't in seasonal production, it becomes more scarce and then requires more resources to obtain than when it's plentiful.
The market availability of a demand, what it takes to produce or procure it, and the subsequent effect that has on prices are all factors in whether something is considered economically scarce.