What exactly? A measure of the selling rate of preowned houses. Includes a geographical breakdown as well as a measure of prices and house inventory (the number of months it would take to deplete the existing supply of preowned houses at the current sales pace).
Source: National Association of Realtors
Released when? On the 25th of the month (or on the first business day thereafter) at 10 a.m. Eastern. Data for prior month.
Market importance: Some. Sometimes moves markets. Timely. Considered a good gauge of near-term spending for housing-related items and of consumer spending in general.
Other notes: Sales of existing (or preowned) houses account for roughly 84% of all houses sold. Sales of new houses account for the other 16%.