Open access (OA) is a set of principles and a range of practices through which research outputs are distributed online, free of cost or other access barriers.[1] With open access strictly defined (according to the 2001 definition), or libre open access, barriers to copying or reuse are also reduced or removed by applying an open license for copyright. Self-archiving by authors is permitted under green OA. Independently from publication by a publisher, the author also posts the work to a website controlled by the author, the research institution that funded or hosted the work, or to an independent central open repository, where people can download the work without paying.Green OA is gratis for the author. Some publishers (less than 5 % and decreasing as of 2014) may charge a fee for an additional service such as a free license on the publisher-authored copyrightable portions of the printed version of an article.If the author posts the near-final version of their work after peer review by a journal, the archived version is called a "postprint". This can be the accepted manuscript as returned by the journal to the author after successful peer review.Journals which publish open access without charging authors article processing charges are sometimes referred to as diamond or platinum OA. Since they do not charge either readers or authors directly, such publishers often require funding from external sources such as academic institutions, learned societies, philanthropists or government grants.
