The undersigned means the person, or the people, who signed a document — used inside the document itself to refer to whoever's name is written at the bottom. It comes with 'the' in front of it, and it works as a noun even though it looks like an adjective: 'The undersigned agrees to pay by the first of each month.' It can be singular or plural, and the verb follows whichever you mean: 'The undersigned hereby confirm...' if two or more people signed. You will also see it as a plain adjective before a noun — 'the undersigned tenant', 'the undersigned parties' — meaning that person is the one who signed below.

The undersignedThe undersigned（以下簽名者）這個詞 means指的是 the person, or the people, who signed a document簽署一份文件的人（一個人或好幾個人） — used inside the document itself用在文件內文裡 to refer to whoever's name is written at the bottom指的就是寫在最下面那個簽名的人。It comes with 'the' in front of it它前面固定會加「the」, and而且 it works as a noun even though it looks like an adjective雖然長得像形容詞，用法卻是名詞: 'The undersigned agrees to pay by the first of each month.''The undersigned agrees to pay by the first of each month.'（以下簽名者同意於每月一號前付款。） It can be singular or plural它可以是單數也可以是複數, and而 the verb follows whichever you mean動詞要配合你指的是單數還是複數: if two or more people signed如果是兩個人以上簽署的話, 'The undersigned hereby confirm...'就用'The undersigned hereby confirm...'（以下簽名者茲確認……）。You will also see it as a plain adjective before a noun你也會看到它當一般形容詞放在名詞前面 — 'the undersigned tenant''the undersigned tenant'（以下簽名的房客）, 'the undersigned parties''the undersigned parties'（以下簽名的各方） — meaning意思是 that person is the one who signed below這個人就是在下面簽名的人。

Two things about how it feels. First, it is a legal and business word, not a talking word. It lives in contracts, formal letters, petitions, affidavits, statutory declarations, and letters of complaint that want to sound serious. Nobody says it out loud about themselves in ordinary conversation.

about how it feels跟這個詞給人的感覺有關的, Two things有兩件事。First第一, it is a legal and business word它是法律和商業用語, not a talking word不是用來說話的字。It lives in它出現在 contracts, formal letters, petitions, affidavits, statutory declarations合約、正式信函、請願書、宣誓書、法定聲明書, and letters of complaint that want to sound serious還有想顯得正式的投訴信裡。in ordinary conversation在日常對話裡, Nobody沒有人 says it out loud about themselves會大聲說這個字來指自己。

Second — and this is the strange part — a writer sometimes uses 'the undersigned' to mean simply 'I', while sounding official and slightly distant: 'The undersigned respectfully requests a refund.' That is old-fashioned, a bit stiff, and today it can read as either very formal or gently joking, depending on who is writing. Modern plain-English legal drafting has been moving away from it in favour of just 'I' or naming the party, so in newer contracts you may meet it less often than in older ones.

Second第二 — and this is the strange part而這是奇怪的地方 — a writer有時候寫的人 sometimes uses 'the undersigned' to mean simply 'I'會用「the undersigned」單純指「我」, while sounding official and slightly distant同時聽起來正式又帶點疏離: 'The undersigned respectfully requests a refund.''The undersigned respectfully requests a refund.'（以下簽名者謹此要求退款。） That is old-fashioned這樣的用法有點過時, a bit stiff也有點生硬, and而 today今天 it can read as either very formal or gently joking讀起來可能非常正式，也可能帶點玩笑意味, depending on who is writing要看是誰寫的。Modern plain-English legal drafting現代講求平易英文的法律寫作 has been moving away from it已經漸漸不用這個詞了 in favour of just 'I' or naming the party改用「I」或直接寫出當事人名字, so所以 in newer contracts在比較新的合約裡 you may meet it less often than in older ones你可能會比在舊合約裡更少遇到它。

Note also that the signing does not have to have happened yet: a blank contract can say 'the undersigned agrees' before anyone has picked up a pen, because the phrase points to the space at the bottom rather than to an actual signature.

Note also that也要注意 the signing does not have to have happened yet簽署這個動作不必已經發生: a blank contract一份空白的合約 can say 'the undersigned agrees'可以寫「the undersigned agrees」（以下簽名者同意） before anyone has picked up a pen在任何人動筆簽名之前, because因為 the phrase points to the space at the bottom這個詞指的是最下面那個簽名的位置 rather than to an actual signature而不是指真正已經存在的簽名。