The term “open access” refers to a free and unrestricted online availability of journal literature, made possible by the convergence of the tradition of scholarly publishing and the technology of the Internet. The specific features of this free and unrestricted availability are spelled out in various public statements, including the Budapest Open Access Initiative, the Bethesda Statement on Open Access Publishing, and the Berlin Declaration on Open Access.
Under the Bethesda and Berlin definitions of open access, it is the author's and copyright holder's responsibility to deposit a complete version of the work and all supplemental materials, including a copy of the permission statement, “in at least one online repository that is supported and maintained by a well-established institution or organization that seeks to enable open access, unrestricted distribution, inter-operability, and long-term archiving.” Under the Bethesda and Berlin definitions of open access, users’ rights consist of “a free, irrevocable, worldwide, perpetual right of access to, and a license to copy, use, distribute, transmit and display the work publicly and to make and distribute derivative works, in any digital medium for any responsible purpose,” as well as “the right to make small numbers of printed copies for their personal use.”
Under the Budapest definition, open access means “free availability on the public internet, permitting any users to read, download, copy, distribute, print, search, or link to the full texts of these articles, crawl them for indexing, pass them as data to software, or use them for any other lawful purpose, without financial, legal, or technical barriers other than those inseparable from gaining access to the internet itself.”
The Public Library of Science (PLoS), an organization of scientists and physicians committed to promoting open access, endorses the Bethesda definition, but allows commercial re-use of its journal content, as specified in the Creative Commons Attribution License (CCAL).
There are several ways to deliver open access. Two frequently cited models of open access are the "green" and the "gold":
The term "Hybrid Open Acess" is also sometimes used to describe an open access model where a journal provides Gold Open Access only for those individual articles for which an open access publishing fee has been paid by the author (or the author’s institution or funder).