The main text of a book or document — the central written content (excluding headers, footnotes, etc.), or the body of a letter.
本文の3ページ目に重要な図表が載っている。
An important chart is printed on page 3 of the main text.
論文の本文と参考文献は別々に書くべきだ。
You should write the main text and the references separately in a paper.
手紙の本文には要点を簡潔に書いた。
I wrote the main points concisely in the body of the letter.
This passage — referring to a particular passage or sentence within a text (i.e., 'this passage/sentence').
問題は本文のこの段落に答えが書かれている。
The answer to the question is written in this paragraph of the passage.
次の設問は本文をよく読んで答えてください。
For the next question, please read the passage carefully and answer.
本文では筆者が環境問題について述べている。
In this passage, the author discusses environmental issues.