Open access (OA) literature is digital, online, free of charge, and free of most copyright and licensing restrictions. By open access to (scientific) literature, we mean its free availability ont he 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.
Suber, Peter (2012): Open Access. Cambridge, Massachusetts, MIT Press. 4 p.
Crawford, Walt (2011): ALA Editions Special Reports : Open Access : What You Need to Know Now. Chicago, American Library Association Editions. 12 p.