This query type will show you which version of your web page is currently in Google's rapid access memory (or “cache”). You'll be able to see the exact date and time at which Google last crawled the page. This is useful for determining whether or not any updates you may have made on your site are visible on Google.
To do a cache query, go to the Google homepage. Enter “cache:” along with the URL of the Web page you want the info for (e.g. cache:http://www.nameadog.com). Note: there can't be any space between the "cache:" operator and the web page URL.
This functionality is also accessible by clicking on the "Cached" link on Google's main results page.