Open Access (OA) refers to the free, immediate, online access to reliable information and research. This information is free from barriers such as paywalls, copyright restrictions, or geographical location.

The different models of Open Access Publishing are described using a colour system: 

Gold OA means to publish immediately free of charge to readers, but authors often pay an Article Processing Charge (APC) to publish. The money for APC's can often come from a funder or institution so authors do not always have to pay out of pocket.

Green OA means to publish in a subscription journal, but making the Author Accepted Manuscript (AAM) available for free in a repository; this is called self-archiving. Green OA is free to the author, but there may be a delay in making it freely available; this is called an embargo.

Hybrid OA means that both open access articles and others only accessible through subscription coexist. An APC is paid for an individual article to be made open access in a subscription journal. 

For more information, check out the Library's web page on Open Access.