Basic terms defined is the newest Joomla! service that allows you to build and maintain a completely free website. The site building software you will be using as part of the service is a slightly modified version of Joomla CMS. The website you create as part of the service will be hosted for free on the special hosting plaform for an unlimited amount of time.

Joomla! CMS is a free open source software developed and maintained for almost 10 years by a community of dedicated volunteers. Its full version is already used by millions of people for creating and maintaining self-hosted websites. is the website of the great community behind Joomla! CMS. On this website you can download the full version of Joomla! CMS, find a detailed documentation on how to use it, get help from fellow users in the community support forums, read the project news, learn about the community events and even get involved in this amazing project.

Differences between and a self hosted Joomla! Site Self-Hosted Joomla Site
Hosting: Free part of the service Responsibility of the user
Domain: Free subdomain at Responsibility of the user
Joomla install: Pre-installed Performed by the user
Joomla updates: Automatic Responsibility of by the user
Languages: All 50+ languaged pre-installed User installs languages as needed
Core Joomla CMS functionality:  Not limited  Not limited 
Extensions: 5 pre-installed extensions No limitations on what user can install
Templates: Limited to a number of pre-selected templates No limitations on what templates user can install
Template files editing: Not possible   Possible
Mailing functionality: Limited   Unlimited
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See full list of the differences between a admin and a self-hosted Joomla admin here.