A Joomla! extension is anything that extends Joomla!'s functionality beyond the core. There are three main types of extension: components, modules, and plugins.
There are also languages and templates, but these are solely designed to modify page output, irrespective of the data being displayed. Although we will discuss the use of translation files and templates, we will not explicitly cover these two extension types in this book.
Tools, sometimes referred to as extensions, are essentially any type of extension that does not fall into the extension-type categories just described. We will not be discussing how to create tools in this book.
Extensions are distributed in archive files, which include an XML manifest file ...