Supply & Demand
The single idea behind nearly every price change you've ever noticed — from surging concert ticket prices to cheaper flights on a random Tuesday.
Game Theory
Game theory explains how two perfectly rational people, each chasing their own self-interest, can still leave each other worse off.
Recessions
Two straight quarters of falling GDP is the popular definition of a recession, but it's not the rule the US officially uses.
GDP
GDP is treated as the single defining number for a country's economic health, yet it says nothing directly about how evenly that wealth is actually shared.
Inflation
A little bit of it, deliberately, is actually the goal — central banks don't aim for zero inflation, they aim for a small, steady amount of it.
Interest Rates
One benchmark number set by a central bank ripples out to mortgages, credit cards, and business loans across the whole economy.