an important day, or a day that you will remember, because of something good that happened then 重要纪念日；喜庆日 birthdays, wedding anniversaries and other red-letter days 生日，结婚周年纪念日和其他以红色表示的日子 It was a red-letter day for United, who won a place in Saturday’s final. 对于曼联来说，这是一个令人陶醉的日子，他在周六的决赛中赢得了一席之地。
Word Originearly 18th cent.: from the practice of highlighting a festival in red on a calendar.