Official name: Advance Monthly Retail Sales
What exactly? A measure of sales at retail establishments. Does not include spending on services.
Source: Census Bureau
Released when? Around the 12th of the month at 8:30 a.m. Eastern. Data for prior month.
Market importance: High. Nearly always moves markets. Very timely -- usually released just two weeks after the month ends. Also sets the tone for personal consumption expenditures to be released later in the month -- and hence gives a peek at a good chunk of gross domestic product.
Other notes: The headline number is the percent change from the previous month, but we also graph the year-on-year change. That way you can see the rate at which sales are increasing or decreasing.