Open access,” that is, means free access not just in the sense of “gratis,” work made available without charge, but also in the sense of “libre” – work that, subject to appropriate scholarly standards of citation, is free to be built upon. This is the cornerstone of the scholarly project: scholarship is written to be read and to influence more new writing.
An important articulation of what open access means via @kfitz who is commenting on the “Berlin-Bethesda-Berlin” agreed upon definition of open scholarly access, part of which reads:
By “open access” to this literature, we mean its free availability on the public internet, permitting any users to read, download, copy, distribute, print, search, or link to the full texts of these articles, crawl them for indexing, pass them as data to software, or use them for any other lawful purpose, without financial, legal, or technical barriers other than those inseparable from gaining access to the internet itself. The only constraint on reproduction and distribution, and the only role for copyright in this domain, should be to give authors control over the integrity of their work and the right to be properly acknowledged and cited. (BOAI)