GDP (Gross Domestic Product)
The total value of everything a country produces.
GDP is the broadest gauge of an economy. Rising GDP signals growth; two straight quarters of decline is a common shorthand for recession.
GDP adds up the value of all the goods and services an economy produces in a period, usually reported each quarter as an annualized growth rate. It is the single broadest read on whether things are expanding or contracting. Economists watch the real figure, which strips out inflation so you are measuring output rather than rising prices.
For markets the release matters most when it surprises. A number well above or below forecast shifts expectations for growth and, through that, for interest rates. The old shorthand that two straight quarters of falling GDP equals a recession is only a rule of thumb; an official US recession call weighs several indicators, not GDP alone.