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. 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. The main focus of the open access movement is "peer reviewed research literature." Historically, this has centered mainly on print-based academic journals. Whereas conventional (non-open access) journals cover publishing costs through access tolls such as subscriptions, site licenses or pay-per-view charges, open-access journals are characterised by funding models which do not require the reader to pay to read the journal's contents. Open access can be applied to all forms of published research output, including peer-reviewed and non peer-reviewed academic journal articles, conference papers, theses,book chapters, and monographs. In the gold OA model, the publisher makes all articles and related content available for free immediately on the journal's website, usually by requiring the author rather than the reader to bear the costs of publication. In such publications, articles are licensed for sharing and reuse via creative commons licenses or similar.The minority of gold open access journals which charge APCs are said to follow an "author-pays" model.