PREAMBLE n. 2 definitions
A introductory portion; an introduction or preface, as to a book, document, etc.; specifically, the introductory part of a statute, which states the reasons and intent of the law.
PROLOGUE n. 2 definitions
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