There should be a course for this! Open Access does not mean free. The Public Library of Science (PLoS) defines Open Access as “unrestricted access and unrestricted reuse.” The Open Access movement founding is often attributed to the Budapest Open Access Initiative (2002) and Peter Suber has written and presented in detail about Open Access. For the most informative and concise overview please read Open Access Overview by Peter Suber.

Nancy K. Herther in her recent post  Scholarly Publishing & Peer Review Face the Future explains the peer review issue with Open Access; and Joe Esposito enumerates some of the complex issues with publishers and Open Access in his post  The Context of Scientific Publishing.

If you prefer your explanation visually, Nick Shockey and Jonathan Eisen, at PHD Comics, explain Open Access for Open Access Week 2012.