Creative Commons & Public Domain

Shared works - whether copyright free or made available under a free license - allow creators and users to share their knowledge and creativity with the world, in the classroom and beyond.
All Rights Reserved - Copyright by default
In copyright law, by default all rights are reserved, or held, for the copyright holder.

Some Rights Reserved - Creative Common licenses
Open licenses, such as those provided by Creative Commons, allow copyright holders to grant permissions to users in a simple, straightforward manner, while still retaining specified rights - some rights reserved.

No Rights Reserved - Public domain
When a work is not protected by copyright (either by design or the expiration of a copyright term) it enters the public domain, a realm where no rights are reserved.

"original CC license symbols by Creative Commons" by Shaddim is licensed CC BY 4.0