The browser cache is a temporary storage location on your computer for files downloaded by your browser to display websites.
Files that are cached locally include any documents that make up a website, such as html files, CSS style sheets, JavaScript scripts, as well as graphic images and other multimedia content.
When you revisit a website, the browser checks which content was updated in the meantime and only downloads updated files or what is not already stored in the cache. This reduces bandwidth usage on both the user and server side and allows the page to load faster. Hence, the cache is especially useful when you have a slow or limited Internet connection.
 -courtesy of Independent Help Ctr.
