Halliday & Matthiessen (2014: 625):
Endophoric reference may point ‘backwards’ to the history of the unfolding text, that is, to a referent that has already been introduced and is thus part of the text’s system of meanings. … This type of endophoric reference is called anaphora, or anaphoric reference, and the element that is pointed to anaphorically is called the antecedent.