What is a literary trend?

A literary trend is, simply put, a very specific, and yet broad, genre. They're very specific because they boil it down to place of origin, era, theme, and then genre. However, as for what qualifies as that theme and genre is vast. For example, Homer's Iliad and Odyssey are both Ancient Greek Epic Poems. The origin(and era) is Ancient Greece, the genre being epic poems, and their theme is, basically, Ancient Greek Gods and Goddesses.