Dictionary.net

The preface or introduction to a discourse, poem, or performance; as, the prologue of Chaucer's "Canterbury Tales;" esp., a discourse or poem spoken before a dramatic performance

One who delivers a prologue.

To introduce with a formal preface, or prologue.

A preface: the introductory verses before a play.

Preface; introduction to a drama.

n. [Greek] The preface or introduction to a discourse or performance, especially, the poem spoken before a dramatic performance or play begins.