Metadata is data that describes data. For instance, it can provide information about
Metadata should comprise an informative headline, an abstract and some keywords.
Most research projects produce thousands of data units. Metadata are the foundation for
Metadata should be comparable and linkable within and across different research projects.
It is therefore necessary to make sure that the notions used to describe the data are consistent and the terminology is clearly defined. For instance, the language of a historical document could be labelled with the terms deutsch or German or deu. According to the ISO 639-3 norm, the only correct option is the last one (see https://de.wikipedia.org/wiki/Liste_der_ISO-639-1-Codes).
Metadata standards offer conventions for the generation and description of research data. They specify and define the structure of metadata.
Search engines for metadata (e.g. http://openarchives.org/pmh/ of the Open Archive Initiative) can find such standardized metadata in repositories of metadata and make the corresponding data available for the research community.
Different metadata standards are used in different disciplines. These links might help you finding a suitable standard or creating, if it does not yet exist:
These links might help you find a suitable standard or create a new one, if necessary: