High mountains and flowing water:
Meaning: In the Spring and Autumn Period, Boya was good at playing the piano, while Zhong Ziqi was good at listening to it. Once, when Boya played the piano, the sound of the piano was like a mountain running water, and only Zhong Ziqi could understand its meaning. Later, people used "high mountains and flowing water" as a metaphor for bosom friends or confidants. It is also used to describe the elegance and exquisiteness of music.