Genres
Mythopoeia
The making of artificial mythologies: fictional myths, pantheons and cosmologies invented whole by a writer, a practice Tolkien named and defended.
Mythopoeia (Greek for myth-making, also mythopoesis) is a subgenre of speculative fiction, and a theme in modern literature and film, in which a writer creates an artificial or fictionalized mythology. The word was recorded as early as 1846, in early use for the making of myths in ancient times; Tolkien popularized the modern practice after a 1931 conversation with C. S. Lewis and Hugo Dyson, writing his poem "Mythopoeia" as a defense of creative myth-making, the act he called sub-creation. William Blake, Lord Dunsany, Lovecraft and the Inklings are its named practitioners.
For novel and web-serial writers, mythopoeia is the deep layer of worldbuilding: the pantheon, the origin stories, the differing accounts cultures tell. Its discipline is internal consistency with in-world variation, myths that contradict each other believably while the underlying truth stays fixed.