DRM, or digital rights management, is a form of protection on electronic works (videos, books, etc.) typically still under copyright. For example, a Kindle ebook is typically a mobi file that needs specific software to make the file readable and it sets limits on how the content can be used and possibly what devices, software, and more can access the content.
Materials without DRM can make something more open (ie, could put it in the realm of Open Access), but it does not remove the copyright on material. Even public domain material could be said to have DRM attached to the content, depending on where it is coming from (think of a Jane Austen novel that is a Kindle ebook. The book is a mobi file that you are paying for a specific type of access to, even though the work should be in the public domain).
DRM comes up in conversation when talking about 'circumvention.' Removing DRM yourself (ie "circumvention") might be a violation of the law. The DMCA limits what you can and cannot circumvent on materials, possibly even if your use of the material would be a fair use.
Material without DRM could be said to be open access material, meaning it is accessible and open if there is no paywall. But, because it is still copyrighted, it does not mean it is Creative Commons or OER material.
See the links below to learn more.
