What is 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 called?

preamble — 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. (Webster's 1913.)