What's a Browser Cache?
Each time you surf the web, your web browser automatically stores local copies of the data that you view. This means that all web pages, documents, graphics or media files that you view in your browser are automatically copied to a special folder on your computer, which the browser uses (no matter what make or computing platform).
Why do Browsers Cache Web Files?
The rationale behind keeping a local copy of a web page ("cached") is that the next time you go to the same web page, your browser will recognize that page and try to open the locally-cached files instead of downloading them again from the remote web server. This is intended to help speed up your browsing experience.
By default, many web browsers try to cache a lot of data. You can change this amount in your browser's settings.
The Downside of Caching Web Files
Sometimes if you're creating a web page (such as a Moodle course), you may want to see the effects of your changes immediately after you make them. However, some web content doesn't always refresh the way you expect when you refresh your browser (aka Refresh, Reload, Ctrl-R, F5, etc.) Some cached items can be a bit stubborn or persistent, and you may refresh or reload a few times and still not see the changes you just made.
Most often, the simplest solution to this persistent cache is to erase or delete your browser's locally-cached files.
How to Erase Your Browser's Cache
Your web browser will have a "Help" option somewhere in its menus. You can search for the term cache and probably find the instructions that you need.
Also, a Google search for clear browser cache will lead you to a number of helpful articles.
Here's one article that covers many different browser makes and version: http://www.wikihow.com/Clear-Your-Browser's-Cache
(Note: When you go to delete your browser's web cache, be careful not to accidentally delete all your browser's history or cookies too, or else your browser may forget the addresses to your favourte websites, or the logins and passwords that you previously asked it to remember for you.)