According to FAIR principles, research data should be understandable to both humans and machines and be: findable, accessible, interoperable with other information systems, reusable by other researchers. FAIR principles are explained in detail in the document FAIR Principles.
You can assess your knowledge using the FAIR-Aware online tool.
Researchers are not left alone in this process—they are supported by repositories that ensure long-term preservation of data.
Many research datasets cannot be opened due to sensitive content, but they should still be properly managed and preserved as FAIR data to allow sharing with other researchers under confidentiality agreements.
It is important to realize that open data is not always FAIR data, and FAIR data may not be open data, and neither says anything about the scientific quality of the data!
The European Commission’s slogan as a science funder is: “As open as possible, as closed as necessary”, but in recent years this has been complemented by the requirement that data must always be FAIR: “As open as possible, as closed as necessary, but always FAIR!”