This document discusses supply and demand in market economies. It defines key terms like market, supply, demand, and how buyers and sellers interact through markets. It explains that supply and demand determine market equilibrium. Demand is defined as the quantity demanded at a given price, and is determined by factors like income, prices of related goods, and expectations. The law of demand and demand curves are described. Changes in demand factors cause the demand curve to shift, while price changes cause movements along a fixed demand curve. Input and output markets are also summarized.