This term has been covered by the website Wikipedia as "Joomla"
This mediawiki site, a `wiki dictionary` about the nature and practice of free improvisation declines to duplicate the content of that listing. Below there is an introduction - a simple copy and paste. from Wikipedia then a link to the Wikipedia entry.
Notes on relevance
joomla is the content management system (CMS) the publishes the website improvisersnetworks.online
Introduction, copied from Wikipedia
Joomla is a free and open-source content management system (CMS) for publishing web content, developed by Open Source Matters, Inc. It is built on a model–view–controller web application framework that can be used independently of the CMS.
Joomla is written in PHP, uses object-oriented programming techniques (since version 1.5) and software design patterns, stores data in a MySQL, MS SQL (since version 2.5), or PostgreSQL (since version 3.0) database, and includes features such as page caching, RSS feeds, printable versions of pages, news flashes, blogs, search, and support for language internationalization.
Over 8,000 free and commercial extensions are available from the official Joomla Extensions Directory, and more are available from other sources. As of 2019, it was estimated to be the fourth most used content management system on the Internet, after WordPress and Drupal.