“Open Access” is a term commonly used for a movement that promotes free availability and unrestricted use of research and scholarship. Open-access (OA) literature is digital, online, free of charge to the reader, and free of most copyright and licensing restrictions, so there are no price barriers and no permission barriers.
The definition of the concept emerged from three conferences:
Green OA publishing refers to the self-archiving of published or pre-published works for free public use. Authors will provide access to preprints or post-prints (pending publisher permission) in an institutional or discipline archive. Examples of green OA include Scholar's Mine and arXiv.org.
Gold OA publishing refers to works published in an open access journal and accessed via the journal or publisher's website. Examples of Gold OA include PLOS (Public Library of Science)and BioMed Central.
Gratis vs. Libre
Gratis OA is information that is available free of charge, while some copyright and licensing restrictions may still apply.
Libre OA is information that is free of charge and free of most copyright and licensing restriction.
While 'free' implies that the information does not cost anything to access, remember that OA publishing still often involves a cost to the author to publish the work.
Open Access Mandates
Research institutions are increasingly adopting mandates that encourage or require researchers to make their findings freely and publicly available.
Open access to research and scholarship is not free—there are costs involved in making research available. The economic models to support unrestricted access to research are still being developed; the common thread among the models is that open access research is available at no charge to all readers.
One model requires a payment when the author submits an article. Usually this charge to publish an open access article is covered by research grant funds. In 2004, one study by Elsevier found that this “author side” payment model encompassed just 17% of open access journals. In an updated study in 2007, Bill Hooker, Associate Editor of BMC Research Notes, conducted a survey of all known open access journals and found that only 18% charged fees.
Other economic models are also being considered. For example, some new open access publishers, such as the for-profit BioMed Central, require author payments, but these payments are waived for institutions that purchase a membership. In other cases, such as the not-for-profit PLoS (Public Library of Science), institutional membership reduces the publication fee for faculty and researchers.
Other titles are subsidized, often by scholarly societies, institutions, or foundations. The 2004 Elsevier study found that government or university subsidies accounted for 55% of the total open access titles, the largest portion. The remaining open access titles (28%) that were not supported by ‘author side’ payments, or by government or universities, were subsidized by paid subscriptions to their print equivalents.
Some journals are entirely open access; every article is available without restriction. Other journals are ‘hybrid’ in that they are traditional subscription-based journals, but offer authors the choice to pay a fee to make their individual article freely accessible to anyone worldwide. The other articles in the journal remain accessible only through subscription. Some publishers offer all their titles under one kind of open access policy, and others have different policies for different titles.
The SPARC Open Access Newsletter (SOAN) is a monthly newsletter authored by Peter Suber and offering news and analysis of the open access movement —the worldwide movement to disseminate scientific and scholarly research literature online, free of charge, and free of unnecessary licensing restrictions.
“Open Access” is a term commonly used for a movement that promotes free availability and unrestricted use of research and scholarship. Open-access (OA) literature is digital, online, free of charge to the reader, and free of most copyright and licensing restrictions, so there are no price barriers and no permission barriers.
Green OA publishing refers to the self-archiving of published or pre-published works for free public use. Authors will provide access to preprints or post-prints (pending publisher permission) in an institutional or discipline archive. Examples of green OA include Scholar's Mine and arXiv.org.
Gold OA publishing refers to works published in an open access journal and accessed via the journal or publisher's website. Examples of Gold OA include PLOS (Public Library of Science) and BioMed Central. 
