The term ‘metadata’ is mentioned in every one of the FAIR principles. Metadata is without question important for findability, accessibility, and reusability, but essential for interoperability. Standardized schemas have been developed by various stakeholders for decades, but too rarely come to practical use. The reason for this is that the application domain is not clearly understood. In many bio-medical research projects, the need for metadata is recognized at some point, but there is not only a lack of overview of existing standards, but also a lack of correct assessment of what individual metadata schemas were actually made for. This paper differentiates different application scenarios for metadata in clinical research.