'Prologue' was the opening of a Greek play before the chorus entered — 'pro-' (before) + 'logos' (word).
A separate introductory section of a literary, dramatic, or musical work; an event or action that leads to a larger or more important event.
From Old French 'prologue,' from Latin 'prologus,' from Greek 'prologos' (a speech before), composed of 'pro-' (before) + 'logos' (word, speech, discourse). In Greek drama, the 'prologos' was the portion of the play before the first entry of the chorus — essentially the opening scene that set the dramatic situation. Euripides was particularly noted