Open Access generally means "available freely to the public via the Internet," which the Budapest Open Access Initiative defines as "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."
Generally speaking, there are two approaches to providing open access:
1) Self-archiving involves the direct deposit of scholarly works into an open repository such as DRUM. It is not a publishing method and its express purpose is to make information as accessible as possible. Self-archived works may be published, to-be-published (pre- and post-prints), or unpublished (many theses and conference papers). This route to open access is known as the Green Road.
2) Publishing in open access journals allows full text access for free. This route is called the Gold Road and complements - does not replace - the Green Road.