Dublin Core (DC

Dublin Core is a very generic metadata scheme for describing all kinds of resources. The scheme (normalized in 2003: ISO 15836) is used in particular by the OAI protocol which allows for “service providers” (for example search engines) to regularly check “repositories” so that their reference bases can be updated. This operation is known as “harvesting”. The international standard OLAC, derived from Dublin Core, allows for properties to be added to the set of descriptors used by Dublin Core.

Dublin Core. A set of 15 descriptors. See also OAI-PMH and OLAC.
Data category, in the context of ISOCat
The DCMI (Dublin Core Metadata Initiative) defines another set of descriptors (qualified Dublin Core) which makes explicit the basic descriptors using about 40 finer-grained categories as well as a certain amount of controlled vocabulary and formal syntax.