Licensing options

To ensure that work is free/open, people should apply a good copyright licence to it. There are two main kinds of free/open copyright licences. 'Copyleft' licences ensure that people (including you) are always free to use the work and works based on it. 'Permissive' licences allow everyone to use the work without passing on that freedom. Copyleft is used by leading community projects such as Wikipedia and GNU/Linux, permissive licences tend to be used more by corporations.

Using an existing licence avoids the risk of legal errors and of problems of compatibility with work under other licences. Cultural works shouldn't be placed under software licences (and vice versa) as the way they are used is different. Remember that free/open licences are copyright licences and do not cover moral rights, trademarks, model releases, publicity rights and other restrictions on using work that may exist.

There are well-recognised definitions of 'free' and 'open' for software: and

The leading software licences are the GNU GPL, a copyleft licence, and the family of licences best represented by the MIT licence, a permissive licence. There are variants of the GPL that are worth investigating as well.

In addition to the definitions of free and open for software, there is one for cultural works:

The best licences for cultural works are Creative Commons ones. But some of its licences are not free/open and so should still be avoided. Creative Commons themselves have identified which of its licences meet the definitions of free and open:

They are the 'Attribution Share-Alike' licence, which is copyleft, and the 'Attribution' licence, which is permissive.

So choose one of these, and specify which one when talking about Creative Commons licensed work rather than confusing people by just saying 'a Creative Commons Licence'.