Ships passing in the night 意為「萍水相逢的人；(因工作或其他因素而) 聚少離多的夫妻或同居男女」，有時亦寫成或說成 ships that pass in the night。譬如說，一對來自不同國家的男女在旅行中邂逅，兩人一見鍾情，在共度一個或兩個禮拜的美好時光後各自返國，從此再也沒有見面，那麼這兩位短暫相遇或只有一面之緣的人就是 ships passing in the night。
這個慣用語最初的用法是 ships that pass in the night，係直接摘錄自美國詩人亨利‧華茲華斯‧朗費羅 (Henry Wadsworth Longfellow) 1863 年出版的詩集《路畔旅舍故事》(Tales of a Wayside Inn)。Ships that pass in the night 一度是比較流行的用法，但現今 ships passing in the night 則較之常用許多。
例句：
- Mary works the early shift and John the late shift. They’re two ships passing in the night. (瑪麗上早班而約翰上晚班。他們是一對聚少離多的夫妻)
- Amy wanted to see Jack again, but to him, they were ships that passed in the night. (艾美想再見到傑克，但對傑克來說，他們只不過是萍水相逢的人)
- Tom and his wife were ships passing in the night as they pursued their separate careers. (由於各有不同的事業，湯姆和他太太聚少離多)
- Like ships passing in the night, the Trump administration and the government of California are cruising in opposite directions on health-care spending. (就像夜間擦肩而過、朝著不同方向前進的船隻，川普政府和加州政府的健保支出政策南轅北轍) (The Daily Breeze)