The word 流行 is formed by combining the character 流 (liú), meaning "to flow" like water or current, with 行 (xíng), meaning "to move" or "to go". Together, they create a conceptual image of something, like water, wind, or news, moving and spreading unobstructed through a wide area or among people. This visual metaphor of fluid, widespread movement directly conveys its core meanings of "to be prevalent", "to be in fashion", or "to be popular", as if a trend is flowing through society.