Wikimedia Commons in the context of MediaWiki markup language

Creative Commons (CC) is an American non-profit organization and international network devoted to educational access and expanding the range of creative works available for others to build upon legally and to share. The organization has released several copyright licenses, known as Creative Commons licenses, free of charge to the public, to allow authors of creative works to communicate which rights they reserve and which rights they waive for the benefit of recipients or other creators. Content owners still maintain their copyright, but Creative Commons licenses give standard releases that replace the individual negotiations for specific rights between copyright owner (licensor) and licensee, that are necessary under an "all rights reserved" copyright management.

As of 2019, there were "nearly 2 billion" works licensed under the various Creative Commons licenses. Wikipedia and its sister projects use one of these licenses. According to a 2017 report, Flickr alone hosted over 415 million cc-licensed photos, along with around 49 million works in YouTube, 40 million works in DeviantArt and 37 million works in Wikimedia Commons. The licenses are also used by Stack Exchange, MDN, Internet Archive, Khan Academy, LibreTexts, OpenStax, MIT OpenCourseWare, WikiHow, TED, OpenStreetMap, GeoGebra, Doubtnut, Fandom, Arduino, ccmixter.org, and Ninjam, among others, and formerly by Unsplash, Pixabay, and Socratic.

MediaWiki is a free and open-source wiki software originally developed by Magnus Manske and released for use on Wikipedia on January 25, 2002, and further enhanced by Lee Daniel Crocker, after which development has been coordinated by the Wikimedia Foundation. It powers several wiki hosting websites across the Internet, as well as most websites hosted by the Wikimedia Foundation including Wikipedia, Wiktionary, Wikimedia Commons, Wikiquote, Meta-Wiki and Wikidata, which define a large part of the set requirements for the software. Besides its usage on Wikimedia sites, MediaWiki has been used as a knowledge management and content management system on websites such as Fandom, wikiHow and major internal installations like Intellipedia and Diplopedia.

MediaWiki is written in the PHP programming language and stores all text content into a database. The software is optimized to efficiently handle large projects, which can have terabytes of content and hundreds of thousands of views per second. Because Wikipedia is one of the world's largest and most visited websites, achieving scalability through multiple layers of caching and database replication has been a major concern for developers. Another major aspect of MediaWiki is its internationalization; its interface is available in more than 400 languages. The software has hundreds of configuration settings and more than 1,000 extensions available for enabling various features to be added or changed.

In mathematics, the quaternion number system extends the complex numbers. Quaternions were first described by the Irish mathematician William Rowan Hamilton in 1843 and applied to mechanics in three-dimensional space. The set of all quaternions is conventionally denoted by ${\displaystyle \ \mathbb {H} \ }$ ('H' for Hamilton) or by H. Quaternions are not quite a field because, in general, multiplication of quaternions is not commutative. Quaternions provide a definition of the quotient of two vectors in a three-dimensional space. Quaternions are generally represented in the form

$${\displaystyle a+b\,\mathbf {i} +c\,\mathbf {j} +d\,\mathbf {k} ,}$$

This is a collection of lists of flags, including the flags of states or territories, groups or movements and individual people.There are also lists of historical flags and military flag galleries. Many of the flag images are on Wikimedia Commons.

The Wikimedia movement is the global community of contributors to the Wikimedia projects, including Wikipedia. This community directly builds and administers these projects with the commitment of achieving this using open standards and software.

First created around and by Wikipedia's community of volunteer editors (Wikipedians), it has since expanded to other projects like Wikimedia Commons and Wikidata and volunteer software engineers and developers contributing to the software used to power Wikimedia, MediaWiki.