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. 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. 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. 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.