When using materials for your courses or even for academic research and publication, you may see work designated with a Creative Commons License.
A creative commons license is a grant of permission from the author to the public (or a segment of the public) to use portions of work otherwise protected by copyright without first obtaining permission from the author (within certain established guidelines).
This may be a good way for educators to share their work freely if they wish to do so.
Just remember that if you put a creative commons license on your work, you are waiving copyright protections for the uses designated in the license.
The creative commons website contains a great description of the types of licenses. Depending on the specification in the license, the user may be permitted to do only certain things with the work (for instance a CC-NC license designates that only non commercial uses are permitted).