From the tutorial on the Mozilla Developer Network site:
HTML5 provides an application caching mechanism that lets web-based applications run offline. Developers can use the Application Cache (AppCache)
interface to specify resources that the browser should cache and make available to offline users. Applications that are cached load and work
correctly even if users click the refresh button when they are offline.
Using an application cache gives an application the following benefits:
- Offline browsing: users can navigate a site even when they are offline.
- Speed: cached resources are local, and therefore load faster.
- Reduced server load: the browser only downloads resources that have changed from the server.