Creative Commons is a nonprofit organization that aims to promote the sharing and reuse of creative works. To this end, they have created a series of licenses that authors can attach to their works to establish rules for how their works can be used and/or shared. All of the licenses require that the creator of the work be attributed, but some of the licenses impose additional requirements:
- NoDerivatives (ND): You let others use your work, but they cannot creative derivative works from it.
- NonCommercial (NC): You let others use your work as long as it is not for commercial purposes.
- ShareAlike (SA): You let others use your work as long as they distribute any derivative works they create from it on the same terms as yours.
You can find more information about Creative Commons licenses and how to share your work with a CC license.
See this discussion of considerations for licensors (those making their work available under a CC license) and licensees (those taking advantage of a work licensed with a CC license). Note that there are possible unintended consequences of using ShareAlike and NonCommercial licenses to license your work:
On the other hand, if you publish a work under a CC license that does not include the NonCommercial provision, you should assume that someone might try to profit from the work, as cited in this recent example (and see follow-up blog entry).
For how to think about sharing a preprint, see How should I license my work on SocArXiv?