Google will soon be introducing a new ‘unavailable_after’ meta tag to allow web masters to advise Google when a particular page will no longer be available for crawling.
For example, if you have a promotion on your website that expires on a specific date, you could use the unavailable_after tag to tell Google when to stop indexing it. The new Google tags are designed to help maintain relevant, up-to-date listings, especially for sites like eBay, so closed auction pages are eliminated from search results.
