This document defines key concepts in microeconomics and macroeconomics. Microeconomics is the study of individual markets, while macroeconomics looks at the overall economy. Positive economics examines what can be proven right or wrong, whereas normative economics is based on opinion. Scarcity exists because resources are limited but demands are unlimited. The four factors of production are land, labor, capital, and entrepreneurship. Opportunity cost refers to the next best alternative forgone when making an economic decision.