Web caching means storing of HTTP response on a temporary basis for the quick retrieval when needed later.
Due to the web caching the number of requests made to the server is drastically reduced because of which the bandwidth consumed is minimized to reduce the web server load. Due to this caching a user can visit a web page even if the web serve is down.
Search Engines, Web Browsers, Content Delivery Networks cache web files.
The cached links show you what a web page looked like the last time Google visited it.
Google takes a snapshot of each web page as a backup in case the current page isn’t available. These pages then become part of Google’s cache. If you click a link that says “Cached,” you’ll see the version of the site that Google stored.
Find out if your web pages are in the Google’s search index using this Google Page Cache Checker.CLICK HERE
Also, SEO siteCheckup has a very good tool for testing the server side caching