Open Access (OA) is the practice of providing unrestricted online access to published and peer-reviewed research, made available free of charge to the reader – to share and re-use without financial, legal or technical barriers (other than access to the Internet).
Gold open access: publishing in OA journals where the article is freely and openly available from the time of publication.
Green open access: making a version of the published article available in a repository like KovsieScholar. The version depends on the publishers' sharing policies. Sometimes we're allowed to archive the final, published version to KovsieScholar, and sometimes we're only allowed to archive a post-print.
Peter Suber, Director of the Harvard Open Access Project (HOAP) defines OA: "Open Access literature is digital, online, free of charge, and free of most copyright and licensing restrictions." This does not mean that copyright is lost or given away. In fact, OA publishing is based on legally open licenses where the author(s) retain copyright and specifies permitted uses. Open licenses, like Creative Commons licenses, are more aligned with academic freedom than traditional copyright where authors mostly sign away copyright to publishers.
Czerniewicz L. & Goodier S. 2014. Open access in South Africa: A case study and reflections. South African Journal of Science. 110(9/10). DOI:dx.doi.org/10.1590/ sajs.2014/20140111