XML documents can have 4 types of entities.

Entities in XML

Entity Description
built-In entity Predefined entities.
character entity Unicode backed entity references.
general entity Entities used to create re-usable sections.
parameter entity Entities used to create sections in DTD's.

Parsed entities in XML

Entity Description
internal entities Entities defined in the XML file. Both general and parameter entities.
external enities Entities defined externally. Both general and parameter entities.

Unparsed entities in XML

Entity Description
notations Declarations of unparsed entities.
data Declarations of unparsed CDATA.
parameter Declarations of unparsed parameter entities.