Creative Commons is an organization that provides researchers, lecturers and others, tools to easily manage their copyright and avoid the need to enter into multiple individual agreements.
Creative Commons License is thus a way to define how your work may be used by others with respect to copyright. One can, for instance, allow for others to share one's texts, adapt or build on them, etc.
One should be aware that Creative Commons licenses cannot be withdrawn. Once your work has been published with a Creative Commons license, then it remains binding.
The licenses consist of four types of right that combine to form six different licenses.
Read report on CC Open content - a practical guide to using Creative Commons licences by Dr. Till Kreuter