This chart shows quarterly U.S. Real (inflation adjusted) Gross Domestic Product that has been Seasonally Adjusted (SA). It is calculated by dividing U.S. Real GDP - Quarterly SA by U.S. GDP Seasonality Factor - Quarterly.
mccormick-charts.com: U.S. Real GDP - Quarterly SA, U.S. GDP Seasonality Factor - Quarterly
Wikipedia: Gross Domestic Product