Economics is the study of scarcity, decision-making, and how people allocate limited resources. It can be divided into microeconomics, which examines individuals and firms, and macroeconomics, which looks at entire markets and the national economy. Demand refers to how much of a product is wanted by consumers, while supply represents how much the market can offer. When demand or supply shifts, the demand or supply curve moves to a new position, impacting the price and quantity in the market.