unprecedented; unheard-of; never before achieved
Used for discoveries, inventions, records, or achievements that no one has ever accomplished before. Often appears in news or formal contexts.
He set an unprecedented record.
This research produced results never before achieved.
前人未到 means 'untrodden' or 'unexplored' (literally 'no person has reached'), often used for physical places or fields of endeavor. 前人未発 emphasizes that something has never been discovered, invented, or achieved before.
未曾有 means 'unprecedented' in the sense of a disaster or extraordinary event. 前人未発 is more about human achievement or discovery.
A yojijukugo (four-character compound) composed of 前人 (previous people), 未 (not yet), and 発 (discover, start). Literally 'not yet discovered by previous people'.