Open Access when applied to scholarly publishing encompasses three related but distinct issues – author rights, accessibility, and user rights.
The purest form of open access advocates unimpeded access to scholarly research in digital format that is free from most copyright and licensing restrictions. This means that the material is available without a subscription charge for anyone to read, download, copy, distribute, print, display and modify. From a practical standpoint this means that anyone with access to the Internet can find and use, to the fullest capacity, any open access publication.
Source: Open Access
Open-access (OA) literature is digital, online, free of charge, and free of most copyright and licensing restrictions.
OA is entirely compatible with peer review, and all the major OA initiatives for scientific and scholarly literature insist on its importance.
From A Very Brief Introduction to Open Access by Peter Suber.