The Application Cache is a new HTML5 capability that is different from the normal browser cache that we’ve had for years. The normal browser cache maintains copies of recent files that you have accessed and keeps copies of those files on your computer so that when you need the same file again, it won’t have to re-download it. Other than some simple browser settings to control the overall cache size and a few meta tags to turn it on and off, you really don’t have any useful control over how it’s used.
The application cache is a web-application-specific cache, the content and behavior of which is controlled by the application itself. The application cache is persistent and provides full off-line capabilities. It is currently supported in Chrome (v4.0+), Safari (v4.0+), Firefox (v3.5+), and Opera (v10.6+). It’s not currently supported in any shipping version of Internet Explorer, but it is coming in IE10.
If you are using Chrome, you can check out what was downloaded at chrome://appcache-internals/: