Herein is a formal, mostly legal or official word meaning “in this” — in this document, this letter, this set of rules, or this situation. A contract might say “the rules herein,” meaning the rules inside this paper. You almost never hear it in ordinary talk; people just say in this letter or in this book.

Herein is a formal, mostly legal or official wordHerein是一個正式、多半用在法律或公文上的字 meaning 'in this'意思是「在這個裡面」 — in this document, this letter, this set of rules, or this situation指在這份文件、這封信、這套規定，或這個情況裡面。A contract might say 'the rules herein,'合約可能會寫「the rules herein」 meaning the rules inside this paper意思是這份文件裡面的規定。You almost never hear it in ordinary talk你在日常對話裡幾乎不會聽到它; people just say in this letter or in this book人們就只會說「in this letter」或「in this book」。

Though actually, students who already know here, there, and where may think herein is only a fancy here. The in is doing real work. It means inside this text or this matter, not “at this spot on the street.” That street meaning is here or hereabouts.

Though actually, students who already know here, there, and where不過其實，已經學過here、there、where的學生 may think herein is only a fancy here可能會以為herein只是比較花俏的here。The in is doing real work那個in其實是在做真正的工作。It means inside this text or this matter它的意思是在這份文本或這件事情裡面, not 'at this spot on the street.'而不是「在街上這個地點」That street meaning is here or hereabouts那種地點的意思是here或hereabouts才有的。

A cluster of old paper words is built the same way: hereinafter, hereof, hereto, herewith. They all sound stiff on purpose. They belong to documents that must not be fuzzy.

A cluster of old paper words is built the same way有一群舊式公文用字也是這樣構成的: hereinafter, hereof, hereto, herewith像hereinafter、hereof、hereto、herewith。They all sound stiff on purpose它們聽起來生硬是故意的。They belong to documents that must not be fuzzy它們屬於那種不能含糊的文件。