never to be seen again; unprecedented and unrepeatable
Often used in the set phrase 空前絶後 (くうぜんぜつご, 'unprecedented and never to be repeated') or as 絶後 alone to describe something so extraordinary it will likely never occur again. Can function as a noun or adverbially.
The concert was an unprecedented and unrepeatable huge success.
His record is said to be something that will never be seen again.
unprecedented and unrepeatable; first and last
Compound of 絶 (ぜつ, 'to cut off, end') and 後 (ご, 'after, later'), literally meaning 'after it ends' or 'nothing after'. The meaning 'never to be seen again' is a natural extension.