Refers to entirely open access peer-reviewed journals, freely available on the internet. Some publishers charge article processing charges (APCs) or fees (APFs).
Refers to Scholarly journal publishers who offer a combination of subscription access and open access. Researchers may be approached by a hybrid publisher to pay a fee for open and immediate access. Sometimes referred to as Bronze when a publisher makes an item open for a short period of time for publicity and exposure.
Refers to pre or post prints which scholarly journal publishers permit researchers to deposit or self-archive in institutional repositories such as Open Access Te Herenga Waka-Victoria University of Wellington; subject repositories such as the arXiv preprint archive in physics, mathematics, computer science and the Social Sciences Research Network (SSRN) which provide free unlimited online access to self-archived versions of publications.
Books can be published as open access; see the Directory of Open Access Books (DOAB), and Knowledge Unlatched
Be aware of unethical and potentially predatory publishers