What exactly? A measure in the change in the market value of goods, services and structures produced in the economy.
Source: Commerce Department
Released when? At 8:30 a.m. Eastern. The first-pass estimate of GDP is called the advance report and is released on the last business day of January, April, July, and October (data for prior quarter). The second-pass estimate is called the preliminary report and is released a month later; the third-pass estimate is called the final report and is released yet another month later.
Market importance: High. The actual pace at which the economy is growing or shrinking -- especially as it relates to expectations -- frequently moves markets.
Other notes: (a) The GDP release also includes a key inflation measure called the price index for gross domestic purchases. It measures the prices of everything -- including imports -- that Americans buy. (b) Personal consumption expenditures typically account for roughly 68% of GDP. Investment, government spending and net exports account for the rest.