Equilibrium occurs in the market when quantity demanded and quantity supplied are equal - where the demand and supply curves intersect. If price is below the equilibrium price, there will be excess demand in the market. Excess demand is a situation in which quantity demanded exceeds quantity supplied. Excess demand puts an upward pressure on prices, which moves themarket towards equilibrium. If price is above the equilibrium price there will be excess supply in the market.
Excess supply is a situation in which quantity supplied exceeds quantity demanded.
Excess supply puts an downward pressure on prices, which moves the market towards equilibrium.