Carroll MW. Creative Commons and the openness of open access. The New England Journal of Medicine 2013;368:789-791
(doi: 10.1056/NEJMp1300040)
The Internet has changed the economics of publication and digital-resource sharing. Copyright law supplies the baseline terms of use for almost all information on the Internet. These terms can be altered if the copyright owner grants a license or permission to do something that would otherwise infringe copyright. Creative Commons licenses are the most widely used of these public licenses for all kinds of copyrighted works except software, for which free and open-source licenses are most common.
http://www.nejm.org/doi/full/10.1056/NEJMp1300040