your browser creates an internal <cache> file for each page that loads, when you return to that page, the browser may check for changes to that internal file. If no changes, then the page loads from that cache file, causing a dramatic speed increase of the browser (in theory) You can usually force the browser to download the page regardless of the cache (some browsers are stubborn about cache files) and the browser will then replace or update that individual cache file (again, in theory) The cache files are (generally) a safe bet to trash for initial troubleshooting of browser problems. Some people disable the cache to prevent the browser from creating cache files, which may be OK for fast internet connections.... Some of this explanation is a little simplistic, but cache files are by their nature temporary, and Windows calls them just that....
