In the markup languages SGML, HTML, XHTML and XML, a character entity reference is a reference to a particular kind of named entity that has been predefined or explicitly declared in a Document Type Definition (DTD). The replacement text of the entity consists of a single character from the Universal Character Set/Unicode. The purpose of a character entity reference is to provide a way to refer to a character that is not universally encodable.
Actually, in XML at least, the term "character entity reference" is incorrect. XML has two relevant concepts:
<, >, &, ", or ';  or   that refers to a character by means of its numeric Unicode codepoint.Although in popular usage character references are often called "entity references" or even "entities", this usage is wrong. A character reference is a reference to a character, not to an entity.