See the replies to this similar question: https://www.researchgate.net/post/What-is-a-open-access-journal-How-can-we-recognize-it-and-what-are-the-benefits-to-publish-a-journal-in-it
Open access journals are journals whose articles are available and reusable worldwide free of charge and without restrictions immediately on publication.
Most open access journals do not charge their authors for publishing articles. In other cases, the so-called author-pays model is common.
The content published in open access journals is searchable in the usual databases and search engines – the Bielefeld Academic Search Engine (BASE) specialises in open access content.
Open access journal (oAJs) These are also referred to as "Gold Road OA". They are journals that provide free access to their articles and the Author pay to publish their works but users access articles without any changes.
Open access journals provide free access to their articles under creative commons licences. Open access journals may be categorised as: pure open access journals and hybrid open access journals. Pure open access journals publish all the articles in a issue as open access, whereas in hybrid open access journals some articles are published as open access.