Hereinafter is even more official than herein.

than herein比than herein（意思是「在本文件中」），Hereinafter is even more official這個字還要更加正式。

It means “from this point on, later in this same document.” Contracts love it because it lets them give a short name and then keep using it: “East Tea Company Limited (hereinafter ‘the Seller’).” After that line, every “the Seller” means that company.

It means "from this point on, later in this same document."意思是「從這裡開始，在同一份文件後面的部分」。Contracts love it合約很愛用它，because it lets them give a short name and then keep using it因為它可以先給一個簡短的名稱，然後一直沿用："East Tea Company Limited (hereinafter 'the Seller')."例如「East Tea Company Limited（hereinafter『the Seller』，即以下稱『賣方』）」。After that line, every "the Seller" means that company那句話之後，每次出現的「the Seller」都是指這家公司。

Though actually, it is not a word for “from now on” in daily life. That is from now on, later, or afterwards.

Though actually不過事實上，it is not a word for "from now on" in daily life它不是日常生活中「從現在起」的用詞。That is日常生活會用的是 from now on、later，或afterwards這幾個字。

Hereinafter only makes sense when there is a written text with a “here” (this document) and an “after” (the rest of the pages). It does not mean “after you die” or “in the afterlife,” and it does not mean “after this meeting” unless the meeting has produced a formal paper.

when there is a written text with a "here" (this document) and an "after" (the rest of the pages)有一份書面文件、裡面有個「here」（指這份文件）和一個「after」（指後面的頁面）的時候，Hereinafter only makes senseHereinafter才說得通。It does not mean "after you die" or "in the afterlife,"它不表示「你死後」或「在來生」，and it does not mean "after this meeting" unless the meeting has produced a formal paper也不表示「這場會議之後」，除非這場會議產出了一份正式文件。

You will see it in contracts, notices, and old-fashioned official English; you will almost never hear a friend say it.

You will see it in contracts, notices, and old-fashioned official English你會在合約、公告和老式的公文英文裡看到它，you will almost never hear a friend say it但幾乎不會聽到朋友這樣說。