What does a simple Joomla! installation include?
From Joomla! Documentation
The "J2.5" namespace is a namespace scheduled to be archived. This page contains information for a Joomla! version which is no longer supported. It exists only as a historical reference, it will not be improved and its content may be incomplete and/or contain broken links.
If you simply install Joomla! without any modifications or extensions, the following (incomplete) list of features will be included.
Joomla 2.5 
- Content component which allows creation and display of "content items" usually in the middle of the page.
- Front page component, which displays multiple recent content items designated as "front page" in the content manager. Configurable for layout and number of items.
- Weblinks component for entering and displaying a list of weblinks.
- Media manager for uploading and managing images and other media.
- User manager (administrative end) and user registration module (front end). Including ACL (Access Control Lists)
- Newsflash module for displaying specific content items as "newsflashes."
- Modules for latest items, most popular, and related items.
- A menu system
- A choice of several templates for your site
- Installers for third party extensions (templates, components, modules and plugins).
- The TinyMCE wysiwyg editor.
- The CodeMirror syntax highlighter editor
- Administrative interface for managing your site