RSS (which stands for, among other things, Really Simple Syndication) that allows you to syndicate your site content. It defines an easy way to share and view headlines and content through newsfeeds. You can find RSS feeds in hundreds of thousands of places on the Internet which allow you to stream their articles into RSS readers - or your Joomla site.

The Feed Display module allows you to display other sites’ RSS feeds on your site, which is a great way to keep your content from being static.

The word "core" in Joomla! pertains to the distributed files which are needed to create and administrate a Joomla CMS powered web site. These files can be downloaded from the Joomla website at http://www.joomla.org/download.html. The Joomla "core" also contains some basic functionality to get new Joomla installations working quickly and easily. Included are the user manager, article manager, weblink manager, category manager, contact manager, and menu manager. There is also a template manager with a few basic templates to power the front-end (website/user) view, a module manager with basic modules, plugin manager with basic plugins, and a few other "out of the box" extensions to extend the functionality of a basic Joomla installation. These core's extensions should not be confused with extensions which are available for downloading from the JED (Joomla! Extension Directory).

Reference: http://docs.joomla.org/Glossary

A block of PHP code that has a name and it has a property that it is reusable it can be executed from as many different points in a PHP Program as required. Also known as a method (if it is inside a class). Most Joomla code is inside functions/methods.