component of metadata. [General Dictionaries] 
n., The markup characters that indicate the start or end of a data element in an SGML-compliant document. A tag serves
as an instruction to a processing or reading program, specifying how the data element is defined or displayed. [Computer
and Information Sciences] 
n., A grouping of metadata elements along with their attributes, such as name, identifier, definition or relationship to other concepts, collated for a specific purpose, community or domain. [Genera