Wikia is a U.S. company that hosts wiki communities at no cost. It was founded by Angela Beesley and Jimmy Wales in October 2004. The project used to be known as Wikicities (while the company that runs it has always been "Wikia"), but the project was renamed to "Wikia" as well in March 2006.
In a nutshell, Wikia is something comparable to Geocities: a free web host (financed by ads in the sidebar) - but the sites they host are wikis and there is no size limit to restrict how big any wiki can grow.
The individual wikis hosted are also known as Wikia (formerly Wikicities).
Wikia hosted the Spanking Art wiki from when it was founded on May 8, 2005 to January 25, 2008, when they shut it down.