Red-letter day
01
記念すべき日, 栄光の日
a day that will always be remembered by an exceptionally good thing that has happened on it
Idiom
例
Today is a red-letter day as we celebrate our company's 10th anniversary.
今日は私たちの会社の10周年を祝う記念すべき日です。
記念すべき日, 栄光の日