Everything you ever wanted to know about open access (but were afraid to ask!)

"OA comes in two main “flavours”: gold and green. With the gold model – which is a business model in its own right – the final version of the article in question is immediately made freely available to anyone upon publication. The cost of publishing the article is recovered upfront by means of an article publishing charge (APC). ...

Green OA on the other hand relies on the traditional subscription model to operate. It allows authors to make a version of the article (usually the accepted manuscript) freely available, for example in their institutional repository, usually after a set period of time – an “embargo period”. As green OA relies on the subscription model and is not a separate business model in its own right, an embargo period is needed to allow the subscription model to operate before free versions of articles are made publicly available...."