excursus

/ɪkˈskɜːsəs/

ot noun

A fuller treatment (in a separate section) of a particular part of the text of a book, especially a classic.
A narrative digression, especially to discuss a particular issue.

Manbalar: Wiktionary (Free Dictionary API orqali), Datamuse, Tatoeba (CC BY 2.0 FR), MyMemory.