An open license is a way for creators to proactively communicate to the public about how copyrighted material can and cannot be used. Open licensing options fill the gap between "all rights reserved" copyright (which protects everything from storing copies of a work to modifying the work) and the public domain (no copyright protection). Popular open licensing mechanisms, such as Creative Commons (CC), allow creators, remixers, and content users to quickly and easily understand how we can legally use and adapt other people's work. CC-licenses are easy to recognize and apply to your own work. A license can be applied to anything copyrightable, such as books, blogs, music, videos, images, software, data, and more!
There are six major CC-licenses that all include different combinations of four basic requirements.
Attribution
You let others copy, distribute, display, and perform your copyrighted work—and derivative works based upon it —but only if they give you credit the way you request. This element is a part of all six licenses.
Non-Commercial
You let others copy, distribute, display, and perform your work —and derivative works based upon it—but for noncommercial purposes only.
No Derivatives
You let others copy, distribute, display, and perform only exact copies of your work, not derivative works based upon it.
Share Alike
You allow others to distribute derivative works only under a license identical to the license that governs your work.
The image above shows the Creative Commons license spectrum between public domain (top) and all rights reserved (bottom). The left side indicates what uses are allowed (e.g., remixing or modifying content) while the right side shows what CC-license components communicate allowable uses. Visit the source for additional information about shading and compatibility with other open licenses, such as the GNU General Public License.