This document provides definitions and explanations of key concepts in macroeconomics including:
1) It defines macroeconomics as the study of aggregate economic variables of an economy. 
2) It explains the circular flow of income and how it refers to the cycle of generation, distribution, and circulation of income between households and production units. 
3) It outlines three methods for calculating national income: the product method, expenditure method, and income method. 
4) Key concepts related to national income are also defined such as GDP, GNP, NNP, consumption and capital goods, as well as stocks and flows.