心照不宣 Tacit understanding
Explanation
彼此心里明白，而不公开说出来。形容双方对某事有默契，不必明说。
Both sides understand it, but it is not publicly stated. It describes the mutual agreement between the two parties about something without saying it.
Origin Story
话说唐朝时期，有一位名叫李白的诗人，他与一位名叫杜甫的诗人，两人都才华横溢，彼此欣赏。有一次，李白和杜甫一起到长安参加科举考试，结果两人都没有考中。李白感到非常沮丧，杜甫则默默地安慰他。他们心照不宣，知道彼此都怀才不遇，因此谁也没有多说什么。后来，两人经常一起游历山水，创作诗歌，他们的友谊也因此而更加深厚。他们的友谊，就像一首无声的诗歌，虽然没有公开宣扬，却早已流传千古，成为后世传颂佳话。
It is said that during the Tang Dynasty, there was a poet named Li Bai and another named Du Fu, both exceptionally talented and admired each other. Once, Li Bai and Du Fu went to Chang'an together to take the imperial examination, but both failed. Li Bai felt very depressed, while Du Fu silently comforted him. They tacitly understood each other, both knowing that they were undervalued, and neither of them said anything. Later, they often traveled together and created poems, strengthening their friendship. Their friendship was like a silent poem. Although it was not publicly known, it has been passed down through the centuries and has become a legendary story.
Usage
常用来形容双方心意相通，不必明说。
It is often used to describe that both parties understand each other well and don't need to say anything.
Examples
-
会议上，领导和下属心照不宣地达成了一致。
huiyi shang, lingdao he xia shu xin zhao bu xuan di dacheng le yizhi
At the meeting, the leaders and subordinates tacitly reached an agreement.
-
他们之间心照不宣，无需多言。
tamen zhi jian xin zhao bu xuan, wuxu duoyan
There was a tacit understanding between them, no need for more words..