Open Access is the:
The power of the Internet and the consent of the author or copyright-holder make OA possible.
Above Definition by SPARC
Want to find out what your favorite journal's open access policy is? Search for the journal title in SHERPA/RoMEO to find out what you are permitted to do with your article post-publication.
Green: archive pre-print, post-print or publisher's PDF
Blue: post-print (final draft post-refereeing) or publisher's PDF
Yellow: pre-print (pre-refereeing)
White: Archiving not formally supported
Remember that you can ALWAYS ask to retain the right to self-archive your article!
See University of Massachusetts Amherst Open Access Policy for example.
The Coalition of Open Access Policy Institutions (COAPI) Toolkit includes a diverse collection of resources related to OA policy initiatives.
We engage and invest in research in order to accelerate the pace of scientist discovery, encourage innovation, enrich education, and stimulate the economy — to improve the public good.
Communication of the results of research is an essential component of the research process; research can only advance by sharing the results, and the value of an investment in research is only maximized through wide use of its results.
The Internet gives us the opportunity to bring this crucial information to a worldwide audience. This has resulted in a call for a new framework to allow research results to be more easily accessed and used — the call for Open Access.
Above from SPARC's Why is Open Access important?
Myth 1 – Open access journals are not peer reviewed.
Myth 2 - All open journals charge publication fees.
Myth 3 - You must choose between prestige and going open.
Myth 4 - Open access is ok for second-rate work, but not first-rate work.
Myth 5 - Post-print archiving violates copyright.
Taken from Danny Kinglsey's "Busting the top five myths about open access publishing".
Further Reading: Boston College's "Open Access Myths: Busted!"