Although there are a great many different definitions in regular everyday use, free content is legally very similar, if not like an identical twin, to open content. An analogy is a use of the rival terms free software and open-source, which describe ideological differences rather than legal ones. For instance, the Open Knowledge Foundation's Open Definition describes "open" as synonymous to the definition of free in the "Definition of Free Cultural Works" (as also in the Open Source Definition and Free Software Definition).Open Definition 2.1 on opendefinition.org "This essential meaning matches that of "open" with respect to software as in the Open Source Definition and is synonymous with "free" or "libre" as in the Free Software Definition and Definition of Free Cultural Works." For such free/open content both movements recommend the same three Creative Commons licenses, the CC BY, CC BY-SA, and CC0.licenses on opendefinition.comCreative Commons 4.0 BY and BY-SA licenses approved conformant with the Open Definition by Timothy Vollmer on creativecommons.org (December 27th, 2013)Open Definition 2.0 released by Timothy Vollmer on creativecommons.org (October 7th, 2014)
