Heather Morrison in a very useful post re-stating the nature of open access states:
There are two basic types of open access:
Open Access Archiving (or the green approach): the author (or someone representing the author) makes a copy of the author's work openly available, separate from the publication process. That is, the article may be published in a traditional subscription-based journal. The version of the article that is self-archived is the author's own copy of the work, reflecting changes from the peer review process (all the work that is provided for free), not the publisher's version.
Open Access Publishing (or the gold approach): the publisher makes the work open access, as part of the process of publication.
However, this is not really the whole story and is in danger of perpetuating the myth that the only form of open access publishing is that made available through the commercial publishers, by author charging. This is why I distinguish between open access through author charging, which is what the Gold Route is usually promoted as being (and which all official bodies from the NIH to the UK research councils assume as 'open'), and the Platinum Route of open access publishing which is free, open access to the publications and no author charges. In other words the Platinum Route is open at both ends of the process: submission and access, where as the Gold Route is seen as open only at the access end.
Harnad has argued that the distinction is unnecessary because at present about half of the Gold Route open access journals do not make author charges. However, if different modes exist we should categorise them clearly and not confuse them: author charging is the publishers' way of maintaining their incomes at the same level as is achieved through subscriptions - rather than being Gold from an open access point of view, we should label it as Brass (Yorkshire dialect for 'money'!), whereas the Platinum Route is the scholar's way of making his/her publications completely open.
We have three ways of achieving open access: archiving, author charging, and completely free - let's make sure the distinction is known and appreciated.