Open Access means free online access to publications.
The Open Access movement was started in 1999 by the Open Archive Initiative. There were different declarations following e.g. 2001 the declaration of the Budapest Open Access Initiative, 2003 the Bethesda Statement and the Berlin Declaration.
The main reason for the Open Access movement might be the journal crisis.
A scientist in an employment under public law uses resources of his organization and places the results of his work at a publisher's disposal for nothing. The peer review of an article again is made by a public financed scientist. The author does not get any fee for his/her publication but has to pay publication charges and to hand over all the rights to the publisher. The journals are subscribed by public financed libraries to make them accessible for the scientists. Because of an annual price increase of an average of 8-10 % by the publishers many libraries are forced to cancel a lot of their journal subscriptions.