Open Access (OA) is the free, immediate, online availability of research articles coupled with the rights to use these articles fully in the digital environment. — Scholarly Publishing and Academic Resources Coalition
Read more: SPARC Open Access factsheet
OA seeks to eliminate barriers to knowledge access and enrich scholarly discourse by widening the scope of participation.
Open Access initiatives exist within a larger movement that includes initiatives around Open Educational Resources, Open Science, Open Data, Open Pedagogy, and more. The common thread among these initiatives is the removal of barriers to education, science, data, pedagogy, and scholarship with the intention that these activities and resources be used to benefit society.
For-profit academic publishing restricts public access to peer-reviewed scholarly research, much of which is publicly funded. In this model, peer review is done by other scholars without compensation and authors don't own the rights to their scholarship.
In 2012, for-profit publishers averaged an 18.9% profit rate, compared with Wal-mart's 3.6% and Exxon Mobil's 10.7%. (Fuchs, C., & Sandoval, M. (2013). The diamond model of open access publishing. tripleC, 11(2).)