The dictionary defines "economics" as "a social science concerned chiefly with description and analysis of the production, distribution, and consumption of goods and services." Here is another definition of economics which I think is more helpful in explaining how economics relates to software engineering.

This definition of economics fits the major branches of classical economics very well. | Macroeconomics is the study of how people make decisions in resource-limited situations on a national or global scale. It deals with the effects of decisions that national leaders make on such issues as tax rates, interest rates, foreign and trade policy. | Microeconomics is the study of how people make decisions in resource-limited situations on a more personal scale. It deals with the decisions that individuals and organizations make on such issues such as how much insurance to buy, which word processor to buy, or what prices to charge for their products or services. | p. 4