Open Access

There are many ways to define open access, but here is the definition given by the Budapest Open Access Initiative:
"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."

• Gold Open Access refers to OA delivered by journals. Some journals ask authors to pay a publication fee called APC (article-processing charge). Journals who do not charge any APC are sometimes called "platinum" Open Access.
• Green Open Access or self-archiving refers to OA delivered by disciplinary or institutional repositories.
• Hybrid journals are subscription journals that give the authors the possibility to make their article open access, generally through the payment of an APC. Some funders (the Swiss National Fund, for instance) do not cover the APCs in hybrid journals. The Plan S funders do not support this kind of publishing.
• Bronze Open Access is used for articles that are made free to read on the publisher's website only without an explicit open license, and could, therefore, lose their OA status later.

• Gratis OA is free of charge, but does not remove any copyright restriction.
• Libre OA is free of charge and also free of some copyright or licensing restrictions. For instance, the Creative Commons CC-BY license allows any use, provided the user attributes the work to the original author.

The open access publishing model is also used for books. Generally, the digital version of the book is open access, sometimes after an embargo period, but the printed version still has to be paid for. A study conducted by the Swiss National Science Foundation between 2014 and 2017 found that making the digital version open access does not reduce printed book sales, and increases the visibility and trackability of the publication. 

The Open Access movement was born as a consequence of the serials crisis, and the development of the World Wide Web, which made the dissemination of academic publications technically easier. Physicists and computer scientists were forerunners, with the creation of arXiv, a preprint repository, in 1991. In the 2000s, the OA movement has been formalised through 3 major declarations, and the number of OA publications has increased noticeably.

On April 1st, 2016, the CODESRIA (Conference for the Development of Social Science Research in Africa) adopted the Dakar Declaration on Open Access Publishing in Africa and the Global South.

• Preprint: before peer review (also known as "author's original manuscript")
• Postprint: after peer review (also known as "author's accepted manuscript" or "author's accepted version")
• Publisher's version or version of record (VoR) : with the layout
• Embargo: the period during which access to the article is limited