surplus and shortage

Surplus and shortage are what you get when the price is in the wrong place — too high, or too low, for the market to clear. A surplus (excess supply) is goods left over: at the going price, sellers offer more than buyers want, so unsold stock piles up. A shortage (excess demand) is the opposite: at the going price, buyers want more than sellers will provide, so the goods run out and people go without or wait in line. Both are signs that the price hasn't yet reached equilibrium.

Crucially, in a free market these states are self-correcting, and the cure is the price itself. Picture bread priced at 5 dollars when equilibrium is 3: sellers bake 100 loaves but buyers want only 60, leaving a surplus of 40. To clear the shelves, bakers cut the price; as it falls toward 3, buyers want more and bakers bake less, and the surplus melts away. Now picture bread at 1 dollar: buyers want 120 but bakers make only 50, a shortage of 70. The price gets bid up; as it rises toward 3, buyers ask for less and bakers make more, and the shortage closes. The gap between the two curves at any wrong price is the exact size of the surplus or shortage.

The honest twist is that surpluses and shortages persist mainly when something stops the price from adjusting. Left alone, markets erase them quickly; but a price ceiling (a legal maximum, like rent control) holds the price below equilibrium and locks in a lasting shortage, while a price floor (a legal minimum, like some farm-support prices or a minimum wage) holds it above and locks in a lasting surplus. So a chronic shortage or glut is usually a clue that a price is being held away from its market-clearing level — by law, by a monopoly, or by sheer stickiness — rather than a failure of supply and demand itself.