Equilibrium
One of the commonest concepts in economics. At its simplest, equilibrium means a balance between the supply of and demand for a good at a market-clearing price. But economists also study equilibria across the entire economy (“general equilibrium”) or in which markets do not clear (see involuntary unemployment). Unhelpfully, equilibria need not be stable (see the commodity cycle) or socially optimal. See also Nash equilibrium. Some economists think too much attention has been given to equilibrium: see this article.