Once in a blue moon
The phrase "once in a blue moon" describes something that happens very rarely, originating from the occurrence of a second full moon within a calendar month. It emphasizes events or experiences that are infrequent and noteworthy due to their rarity. Whether it's a rare celestial event or an unusual personal encounter, these moments often revive nostalgia and highlight the passage of time. Over time, the phrase has propagated into everyday language, symbolizing the value of unique occurrences amidst the routine of daily life.