Creative Commons is a nonprofit organization that enables the sharing and use of creativity and knowledge through free legal tools. Creative Commons licenses are not an alternative to copyright. They work alongside copyright and enable you to modify your copyright terms to best suit your needs. -- From Creative Commons website
A Creative Commons license lets creators decide which rights they would like to keep, and it clearly conveys to those using their work how they’re permitted to use it without asking the creator in advance. Ideally, OER content includes the least restrictive Creative Commons license, CC-BY, which only requires proper attribution. Users are otherwise permitted to copy, distribute, and adapt the work as they like.