A threepeat refers to the accomplishment of winning a championship or achieving a particular feat three times consecutively. In the context of the clue, it refers to the Green Bay Packers winning the championship three times in a row during the specified periods.
Note: The provided meaning of the answer is for the latest New York Times crossword puzzle clue: Winning feat achieved twice by the Green Bay Packers (1929-31, 1965-67). Explanations are generated by AI and may be inaccurate.