noun
In music, the opening section of a piece or movement before the main theme.
この交響曲の導入部はとても静かだ。
The introduction of this symphony is very quiet.
noun
General use for the opening section of a speech, article, presentation, etc.
論文の導入部で研究の目的を説明する。
In the introductory part of the paper, I explain the purpose of the research.
スピーチの導入部で聴衆の注意を引く。
The lead of the speech grabs the audience's attention.
前書き is a preface or foreword, usually written by the author, whereas 導入部 is the actual beginning of the main content.
Compound of 導入 (どうにゅう, 'introduction, bringing in') and 部 (ぶ, 'part, section').