"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." (quoted from A Very Brief Introduction to Open Access by Peter Suber)
The Open Access movement promotes the practice that scholarly publications are made available online without prohibitively high access costs and stringent copyright and licensing restrictions. It facilitates quicker and broader dissemination of knowledge by removing the price and permission barriers to research outcomes.
Open Access is compatible with features of traditional publishing such as peer review, journal prestige, and researchers' career advancement.
These books provide excellent introduction to open access:
