Different levels of openness exist. These are largely dictated by publisher policies and the ways in which published material is accessible. It does not always mean the work is in the public domain; in many cases open access means the work has been assigned a license by its copyright holder granting permissions for others to reproduce and redistribute their work,
Gold OA refers to publications that are 100% free and accessible to all. Some Gold OA journals require the authors to pay a fee to support this model read more under this guide's section on paying for open access.
Green OA refers to publications that are available as pre-prints, hosted in an institutional or subject repository, but the copyright of the final published manuscript belongs to the publisher. This model usually does not require authors pay a fee; authors need to discuss this option with their journal.
It is easy to confuse "Public Access" and "Open Access" -- if your research is funded by a federal agency that requires "Public Access", then this refers to the depositing of your final peer-reviewed version of the author manuscript into a public access repository (e.g., NIH PubMed Central, NSF Public Access Repository (NSF-PAR), Department of Energy PAGES, etc.) within a certain time frame. While the articles in these online repositories are publicly available and free to read, the copyright for many of these works are owned by the journals and may have some restrictions on their use. Any uses beyond fair use would require you to get permission from the copyright holder.
Please contact Public_Access@Brown.edu for assistance understanding your funders' public access policy.