A masterpiece; an outstanding work of art or craft.
彼の最新作は評論家から傑作だと評された。
His latest work was praised as a masterpiece by critics.
この映画は間違いなく彼の傑作だ。
This film is undoubtedly his masterpiece.
あの画家の傑作が美術館に展示されている。
The painter's masterpiece is on display at the museum.
(Jocular/dated) Used ironically or humorously to refer to a ridiculous blunder or outrageously funny thing.
あのプレゼンの準備不足ぶりは傑作だったよ（皮肉）。
The lack of preparation for that presentation was a real doozy (sarcastically).
彼の言い間違いは会場を爆笑させる傑作だった。
His slip of the tongue was a hilarious blunder that made the audience roar with laughter.