"Open Access is a means of disseminating scholarly research that breaks from the traditional subscription model of academic publishing. It has the potential to accelerate greatly the pace of scientific discovery, encourage innovation and enrich education by reducing barriers to access. Open Access shifts the costs of publishing so that readers, practitioners and researchers obtain content at no cost.
However, Open Access is not as simple as “articles are free to all readers.” Open Access encompasses a range of components such as readership, reuse, copyright, posting and machine readability. Within these areas, publishers and funding agencies have adopted many different policies, some of which are more open and some less open." ( from How Open is it? SPARC, PLOS, OASPA)