"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."
The original definition of open access covered journal articles, but it's meaning has expanded to cover a much broader range of scholarly outputs, such as books, proceedings, protocols, data sets, software code, graphics, sound recordings, etc.. Open access covers author control over their work AND permissions for what the user can do with the work. These are codified with Creative Commons licenses. Open access means there is no cost to the user. However, review, production and distribution of scholarship still incur costs which may be covered in myriad ways.
Scholarly works may be published open access in several ways. Publishers, libraries and OA advocates use a color-coding system to describe them.
Gold - the publisher makes the article and related content freely available to users immediately upon publication on their website based on payment of an author processing charge (APC). Articles are licensed for sharing and reuse.
Green - authors are permitted to self-archive a pre- or post-print of their work by the terms of their author agreement with the publisher or under an institutional policy. UMass Amherst's Open Access Policy enables all faculty to openly archive their published articles.
Hybrid - this refers to mix of open and paywalled content in a journal. The publisher pays for the journal issue through a combination of subscription and APC fees.
Diamond/platinum - article and journal publication is paid neither by the user nor the author but rather by an academic institution or consortia, a learned society, a philanthropist, a government grant or some other third party.
The UMass Amherst Libraries have been advocates for open access investments, policies and services coordinated through the Office of Scholarly Communication. These include: