An open license or free license (licence in Commonwealth English) is the legal statement that allows free content and free software to be "free". This means "free" as in "freedom of speech" or "free to use it how you want". See the Freedom Defined wiki for more information.
The exact meaning may vary, but a common idea of an open license is one that requires attribution but otherwise lets people use the content in any way, including commercially, only requiring them to share their modifications under the same license (copyleft/ShareAlike). This corresponds to CC-BY-SA or GFDL.
In more detail, the main point of an open license is to tell people that they are free to use the content, under relatively few conditions:
- The most common condition is attribution - all CC licenses contain this. The public domain tools CC0 (CC Zero) and public domain certification do not, but they are declarations and not licenses.
- The next most common condition is Share Alike - that you will share, as long as the final product is also shared in the same way.
Non-commercial licenses - not "free"
However, content with this license is not considered "free" by Freedom Defined (the free cultural works definition), or the Open Knowledge Definition and is not able to be used in a site such as Appropedia which uses a license allowing commercial use.
This may be a wise choice for personal photos, or in some cases for creative work that you may wish to make a profit from.
List of licenses
There are many free licenses, but the most common are:
- CC-BY-SA - Creative Commons, By Attribution, Share Alike
- CC-BY - Creative Commons, By Attribution.
- Public domain - not actually a license, this is the absence of any copyrights, license, or restriction of any kind.
(See also the list of licenses at opendefinition.org.)