Short answers, pulled from the story.
Economics is a social science that studies the production, distribution, and consumption of goods and services. The term derives from the Ancient Greek oikonomia, meaning the way to run a household, the know-how of an oikonomikos or household manager. The earlier name for the discipline was political economy, but since the late 19th century it has commonly been called economics.
Lionel Robbins in 1932 defined economics as the science which studies human behaviour as a relationship between ends and scarce means which have alternative uses. He called the definition analytical rather than classificatory, focusing on the aspect of behaviour imposed by scarcity. This has been termed perhaps the most commonly accepted current definition of the subject.
Microeconomics analyses the basic elements of economies, including individual agents such as households, firms, buyers, and sellers, and the markets in which they interact. Macroeconomics examines economies as whole systems, studying aggregates like national income, the unemployment rate, and inflation, along with monetary and fiscal policy.
Thomas Carlyle coined the dismal science in 1849 as an epithet for classical economics. The phrase is commonly linked to the pessimistic analysis of Thomas Robert Malthus, who in 1798 argued that population grows geometrically while food grows arithmetically, pushing wages down to subsistence.
John Maynard Keynes ushered in contemporary macroeconomics with his 1936 book The General Theory of Employment, Interest and Money. Written during the Great Depression of the 1930s, it argued that high unemployment might not be self-correcting because of low effective demand, and it advocated active monetary and fiscal policy responses.
The production-possibility frontier is a graphical representation of scarcity, opportunity cost, and efficiency, often illustrated with two goods such as guns and butter. Its negative slope means producing more of one good requires producing less of the other. A point inside the curve represents inefficiency, such as high unemployment during a recession, while a point beyond it is wanted but unreachable.