There are 2 (two) types of open access
a. Gold open access: As per Elsevier
• An author can publish in an open access journal or hybrid journal which supports open access.
• The published article is freely available to everyone but the author can choose commercial or non-commercial Creative Commons license.
• If there is fee then publishing cost should be covered by the author or the institution or funding agency.
• All the open access journals can be found on the Directory of open access journals (https://doaj.org).
• DOAJ contains the journals in various 80 languages from 126 countries having 16665 journals and 6376560 articles till date.
b. Green open access: As per Elsevier
• The article can be published under a subscription model by linking and self-archiving the article for sharing as per policy.
• All accepted manuscripts should have Creative Commons use license, thus author retain the right to the article for further use.
• No fee is required to pay by the author for the publication as it is covered under the subscription.
• All the self-archiving publishers with policies can be found of SHERPA/RoMEO database.
• Open Access SHERPA-RoMEO project for free self-archiving.
• Sharing the research information, freely in the form of article/paper
• Self-archiving also known as "Green Open Access" in institutional repository.
• SHERPA project commenced in 2002 by JISC and CURL
• RoMEO is Publisher's copyright and archiving policies
• This project is backed by UNESCO.
