An entity used to represent information within the context of a document type definition. Parameter entities may be used to link the content of additional DTD files to a DTD, or as an abbreviation for frequently repeated declarations. Parameter entities are distinguished from general entities by their use of a percent sign (%) rather than an parent element of the SECOND element.
An entity that consists of DTD specifications, as distinct from a general entity. A parameter entity defined in the DTD can then be referenced at other points, in order to prevent having to recode the definition at each location it is used.
An entity used exclusively within a DTD, never in a document.