Open Access (OA) publications are freely available online for anyone, anywhere, and at any time. In an OA model, all costs associated with the added value provided by publishers are covered up front. The content is delivered at no cost to the reader and without restrictions, expanding access to literally anyone with an Internet connection and an interest in a given topic. This is an especially salient point for authors of scientific content.
There are two routes to open access: the gold and green model.