noun which may take the genitive case particle 'no'
certified; guaranteed (genuine)
Originally referred to an item with a certificate of authenticity, especially in art or antiques. Now used more broadly for something acknowledged as the real thing or of assured quality.
See also: 極め付きの品
この茶碗は極め付きの品で、箱書きもある。
This tea bowl is a certified piece, complete with a box inscription.
noun which may take the genitive case particle 'no'
Describes someone or something widely recognized for a particular quality, whether positive (acclaimed) or negative (notorious). Often used in the pattern ～の極め付き.
彼は正直者の極め付きだ。
He is an acknowledged man of integrity.
あの店はまずさの極め付きで有名だ。
That restaurant is notorious for its terrible food.
noun
pièce de résistance; the best (or worst) example
Colloquial use as a noun, often in the pattern ～の極め付き, to mean the ultimate or most outstanding example of something, whether good or bad.
この料理が今日の極め付きだ。
This dish is the pièce de résistance of today's meal.
折り紙付き also means 'certified' or 'guaranteed', but it derives from the practice of attaching a folded paper certificate. 極め付き emphasizes the judgment or appraisal itself, while 折り紙付き focuses on the physical certification.
From 極め (kiwame, 'conclusion' or 'judgment') + 付き (tsuki, 'attached'). Originally referred to an appraisal certificate attached to an artwork or antique, certifying its authenticity and value.