The first open access initiative, Budapest Open Access Initiative, which took place in 2002, defined two ways of providing Open Access: (1) by publishing in open access journals, and (2) by self-archiving articles in open access digital repositories.
Archiving scholarly articles in university repositories became a mandate (with an "opt-out" provision to be used as needed) for faculty in much of Europe, but in the U.S., it was not until after 2008, when the Harvard University Faculty of Arts & Sciences voted to adopt an "opt out" OA policy that the Harvard Model Open Access Policy began to be adopted in many U.S. universities.
What Does Open Access Mean?
Open-access (OA) literature is digital, online, free of charge, and free of most copyright and licensing restrictions.
OA removes price barriers (subscriptions, licensing fees, pay-per-view fees) and permission barriers (most copyright and licensing restrictions). The PLoS shorthand definition —"free availability and unrestricted use"— succinctly captures both elements.
There is some flexibility about which permission barriers to remove. For example, some OA providers permit commercial re-use and some do not. Some permit derivative works and some do not. But all of the major public definitions of OA agree that merely removing price barriers, or limiting permissible uses to "fair use" ("fair dealing" in the UK), is not enough.
Here's how the Budapest Open Access Initiative put it: "There are many degrees and kinds of wider and easier access to this literature. By 'open access' to this literature, we mean its 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 only constraint on reproduction and distribution, and the only role for copyright in this domain, should be to give authors control over the integrity of their work and the right to be properly acknowledged and cited."
Here's how the Bethesda and Berlin statements put it: For a work to be OA, the copyright holder must consent in advance to let users "copy, use, distribute, transmit and display the work publicly and to make and distribute derivative works, in any digital medium for any responsible purpose, subject to proper attribution of authorship...."
The Budapest (February 2002), Bethesda (June 2003), and Berlin (October 2003) definitions of "open access" are the most central and influential for the OA movement. Sometimes I refer to them collectively, or to their common ground, as the BBB definition.
When we need to refer unambiguously to sub-species of OA, we can borrow terminology from the kindred movement for free and open-source software. Gratis OA removes price barriers alone, and libre OA removes price barriers and at least some permission barriers as well. Gratis OA is free of charge, but not free of copyright of licensing restrictions. Users must either limit themselves to fair use or seek permission to exceed it. Libre OA is free of charge and expressly permits uses beyond fair use. To adapt Richard Stallman's famous formulation (originally applied to software), gratis OA is free as in beer, while libre OA is also free as in speech.
In addition to removing access barriers, OA should be immediate, rather than delayed, and should apply to full texts, not just abstracts or summaries.