a preliminary discourse; a preface or introductory part of a discourse, poem, or novel.

an introductory speech, often in verse, calling attention to the theme of a play.

the actor or actress who delivers this.

an introductory scene, preceding the first act of a play, opera, etc.

any introductory proceeding, event, etc.

Appetizing delicacies were the prologue to a long dinner.

to introduce with or as if with a prologue.

noun

beginning , exordium , explanation , foreword , introduction , opening , overture , preamble , prelude , proem , prolegomenon , induction , lead-in , preface , prolusion