On this "Open access" page:
Open access is usually a term associated with peer-reviewed journals, but it can be applied more generally, as well, to books and other materials. The open access symbol is a lock that has been opened.
Open access (OA) refers to online research outputs that are free of all restrictions on access (e.g. access tolls or subscriptions). Open access can be applied to all forms of published research output, including peer-reviewed and non peer-reviewed.