Excursus

An excursus (from Latin excurrere, "to run out of") is a short episode or anecdote in a work of literature. Often excursuses have nothing to do with the matter being discussed by the work, and are used to lighten the atmosphere in a tragic story, a similar function to that of satyr plays in Greek theatre. Sometimes they are used to provide backstory to the matter being discussed at hand, as in Pseudo-Apollodorus' Bibliotheke. Furthermore, an excursus is often applied to a piece of academic writing to provide digressive information, which does not contribute directly to the line of argument, but can still be linked with the overall topic of the text.