“Open-access (OA) literature is digital, online, free of charge, and free of most copyright and licensing restrictions. What makes it possible is the internet and the consent of the author or copyright-holder.”
Peter Suber, A Very Brief Introduction to Open Access
(http://legacy.earlham.edu/~peters/fos/brief.htm)
While OA is a newer form of scholarly publishing, many OA journals, textbooks, and monographs comply with well-established peer-review processes and maintain high publishing standards. For more information, see Peter Suber's overview of Open Access: http://legacy.earlham.edu/~peters/fos/overview.htm.