Authors publish in a subscription journal, but also make their articles freely accessible online, either by placing them in an institutional repository, like the Research Repository @ WVU or in a central repository such as PubMed Central, Research Gate, Mendeley, etc.
Authors publish in open access journals that make their articles freely accessible online immediately upon publication. Open access journals conduct peer review and allow authors to retain their copyright. These journals sometimes meet their expenses by charging the author a publication fee. Examples of widely recognized scholarly OA publishers are BioMed Central and Public Library of Science (PLoS). There are currently over 13,000 OA publications listed in the Directory of Open Access Journals.
Some traditional, subscription-based publishers have introduced a "hybrid open access" concept. In this model, the publisher will make an article immediately available to the public if the author pays an additional open-access fee. Frequently referred to as an "open choice" or "paid access" charge, these fees can range from $500-$3,100 per article. Publishers participating in this model include Elsevier, Springer, and Wiley.