Open Access a movement that started 20 years ago. The mandate of this movement is for free access to Scholarly information. This refers to digitally available information to be freely accessible with no cost, free of most copyright & license restrictions.
The literature that should be freely accessible online is that which scholars give to the world without expectation of payment. Primarily, this category encompasses their peer-reviewed journal articles, but it also includes any unreviewed preprints.
Further reading: COKI: Open Access Dashboard
The golden route:
Full Open Access journals: publication via publisher platforms, in fully open access journals. This route may involve a charge. The publication costs, known as ‘article processing charges (APCs), are covered by authors or by their institutions.
The green route:
the full text of academic publications is deposited in a trusted repository, a publicly accessible database managed by a research organization.
The Hybrid
publication via ‘hybrid’ journals. These journals are subscription journals that allow open access publication of individual articles on payment of an Article Processing Charge (APC)