"Open access (OA) literature is digital, online, free of charge, and free of most copyright and licensing restrictions."
-Peter Suber, Open Access, 2012
Unlike material in the public domain, some open access articles, books, videos etc. may not be manipulated or used for profit. Some articles may have re-use restrictions that will be indicated by a Creative Commons license (CC).
The Open Access movement began as a way to share research that avoids the barriers and costs of typical publication. Academic libraries may offer many of the journals that students need for research; however, for those outside of academia, those same journals are now unavailable without paying a costly fee. Articles published in Open Access journals facilitate a wider conversation, and make important research available to the general public. This is particularly important for scientific and medical research, where shared data can lead to potential innovations that affect all our lives.
Gold OA: The term used for open access journals.
Although all of these journals are (or claim to be) peer reviewed, keep in mind that there are levels of quality for scholarly publications. One method for assessing quality is to look at Beall's List of potential, possible, or probable predatory scholarly open-access publishers. Some of the markings of a predatory journal are poor quality standards, mismanagement, and costly author fees. The criteria for determining these journals specified by Beall's List is here. If you are still unsure of the quality of a specific journal, please ask a librarian.
Example of an OA journal: BioMed Central
See a full list of open access journals in the Directory of Open Access Journals (DOAJ)
Green OA: The term used for articles that are available through an institutional repository or a personal archive.
Articles available in OA repositories are typically a version of an article that is published or will be published in a scholarly journal (a "preprint" or a "postprint" of an article), but not necessarily so. A preprint is an author draft, and a postprint is a peer-reviewed version of the article before final publication.
An example of an Institutional Repository (IR): Institutional Repository at the University of Florida (IR@UF)
Browse the Directory of Open Access Repositories (Open DOAR) for a full list.