What is metaphor?

Noumenon and vehicle both appear, and the metaphor words "Shi", "Xiang" and "Cheng" are commonly used in the middle, sometimes without metaphor words. The typical form of metaphor is the phrase "jumping into a boat in white rain" (Su Shi's drunken book at the Lake Building). "Rain" is noumenon, and "bead" is metaphor. There are no words like "yes" and "Zuo", and there is no "image", but we can see that Su Shi compares "rain" to "pearl" and substitutes it into the context here. This is a metaphor.