"Open-access (OA) literature is digital, online, free of charge, and free of most copyright and licensing restrictions.” (Peter Suber)
*OA removes price barriers (subscriptions, licensing fees, pay-per-view fees) and permission barriers (most copyright and licensing restrictions).
History of OA:
The Budapest Open Access Initiative in 2002 was the first global Open Access initiative. Attending scientists were asked to sign an agreement to preferentially publish their findings in open access journals. This agreement can still be signed online today. In 2003, the Berlin Declaration on Open Access to Knowledge in the Sciences and Humanities was published after a Conference with that name.