Table 1. Types and definitions of open access publishing.

Category	Definition
‘Free’ gold OA	Article published in a journal that does not charge authors an APC; the article is freely available to all readers immediately.
APC Gold OA	Article published in a journal that charges publishing authors an APC; the article is freely available to all readers immediately.
Delayed OA	Article published in a subscription-based journal; the article is freely available to all readers after an initial closed/paywalled period; also known as a moving paywall.
‘Hybrid’ publication	Article published in subscription-based journal; the article is freely available immediately to all readers if the publishing author pays an APC; hybrid articles are published alongside paywalled articles whose authors did not pay the APC.
‘Closed’ subscription-only publication	Article published in a subscription-based journal that does not offer the APCs; article is never freely available.
Green OA	Article is made freely available, irrespective of where it is published, by posting a copy in a subject or institutional repository or on another website.