In music, the opening section of a piece or movement before the main theme.
The introduction of this symphony is very quiet.
General use for the opening section of a speech, article, presentation, etc.
In the introductory part of the paper, I explain the purpose of the research.
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').