Prologue

A prologue or prolog from Greek πρόλογος prologos, from πρό pro, "before" and λόγος logos, "word" is an opening to a story that establishes the context and gives background details, often some earlier story that ties into the main one, and other miscellaneous information. The Ancient Greek prólogos included the modern meaning of prologue, but was of wider significance, more like the meaning of preface. The importance, therefore, of the prologue in Greek drama was very great; it sometimes almost took the place of a romance, to which, or to an episode in which, the play itself succeeded.
 * Precambrian worm