Help:Legal issues for editors
The Wikimedia Foundation hosts its project sites under the terms of United States law, and editors are asked to be considerate of the potential legal implications (both to themselves and to the Foundation) inherent in their activity on any Wikimedia site.
The various Wikimedia projects seek to distribute information under a free license (sometimes known as "copyleft"). This means that the content on Wikimedia projects, in most cases, may be copied and reused elsewhere, just so long as the content is attributed to its authoring source, and that the ensuing copy of the content is also similarly released under free license.
In 2009, the Wikimedia Foundation pushed through an update to the legacy GNU Free Documentation License, such that the Creative Commons Attribution-ShareAlike (CC-BY-SA) license is now used alongside the GFDL. When bringing new content into publication on any Wikimedia project, don't just copy and paste without attributing the author. That is plagiarism, and it is not only ethically wrong, it potentially brings legal risk to yourself and possibly the Wikimedia Foundation. Rights-reserved copyright is an honorable tradition, too, and it should be respected.
Watch the policies of the site that you are working on. Depending on the project site, you may be assigning the copyright to the public domain, or you may retain the copyright, but under specific terms of re-use. Because of the free-wheeling activity on a wiki, it is potentially "easy" to violate the copyright of others, but this should never become the rule.
While Section 230 of the United States code under the Communications Decency Act does provide certain protections from civil libel and defamation cases for the hosts of interactive computer content, no similar law protects the individual who willfully acts to improperly defame or libel another individual or corporation on an Internet site or forum. That is, if you elect to use a Wikimedia Foundation website as a platform to defame or libel someone, the United States law will largely shield the Wikimedia Foundation from prosecution, but will do nothing to protect you from prosecution. In fact, in order to comply with Section 230, the Wikimedia Foundation will likely assist the prosecution in rendering identifying server information that would assist in bringing the perpetrator to justice.