Gross Domestic Product (GDP), explained.
The total value of goods and services an economy produced. Usually reported as the change from the previous quarter (or annualised in the US).
Why it moves markets
It's the broadest picture of growth. Markets often care more about whether it beats or misses forecasts, and about the first estimate, than about later revisions.
Who publishes it, and when
National statistics agencies. Quarterly in most economies (the UK and Canada also publish monthly GDP). Usually an advance estimate, then revisions.
Pairs that often react
Pairs that include the currency involved usually react most. How much and in which direction depends on the surprise against expectations and on everything else going on. This isn't a prediction.
Educational only. Not advice and not a signal. Spreads often widen and prices can gap around big releases.