Literature, like any other field, has its own terminology. Allusion, metaphor, onomatopoeia -- there are many words that help define common stylistic modes or specific techniques that a writer may use in the construction of a story. One of the oldest of these terms describes a narrative that begins with the action already in progress, a technique referred to as "in medias res."
"In medias res" is a Latin term, which roughly translated, means “in the middle of things.” The term first appears in the Ars Poetica, a treatise written around 15 B.C. by the Roman poet Horace. In this seminal work, Horace offers advice to poets and orators, defining best practices for prospective writers. Citing Homer’s epic poem "The Iliad" as an example, Horace notes that the great poem begins right in the middle of the story, rather than at the beginning, thus pulling the reader into the action and creating instant interest.
Ever since Horace coined the term so long ago, many critics have found "in medias res" useful in describing the common practice of starting a story in the middle of the action. While its original reference was to the tradition of epic poetry, in modern times, the term has been applied not only to poems but also to novels, movies and other forms of narrative.