Open Access is "the free, immediate, online availability of research articles, coupled with the rights to use these articles fully in the digital environment." (SPARC website) Open Access, or "OA" removes all barriers for readers of articles and other scholarship. The most common barriers are cost restrictions and use restrictions.
Please see an excellent overview of Open Access written by Peter Suber, Director of the Harvard Office for Scholarly Communication: http://legacy.earlham.edu/~peters/fos/overview.htm.
There are two main types of OA.
"Gold" OA is scholarship published in Open Access journals. These journals include peer review, just like subscription journals. Authors often (but not always) must pay a fee to publish their work in OA journals. TCU supports publishing in Open Access journals through our Open Access Fund.
"Green" OA is scholarship that is published through university- or subject-based repositories. TCU such a repository at the following website: https://repository.tcu.edu/