For scholarly work Open Access (OA) means free, immediate, permanent online access to the full text of peer reviewed literature for anyone connected to the internet.
Other definitions:
SPARC: Scholarly Publishing and Academic Resources Coalition (200+ members are primarily academic and research libraries located in the U.S. and Canada)
EPrints (open-source digital repository platform developed at the University of Southampton)
Australasian Open Access Strategy Group (supported by ten Australian and eight New Zealand Institutions with a commitment to Open Access)
OpenSource.com (a community resource)
Other important organizations defining open access in academia:
OApen.org (The National Library of the Netherlands)