The Chinese word 下流 (xiàliú), meaning "indecent" or "vulgar", is formed through a metaphorical and semantic shift from its original literal components. Literally, 下 means "below" or "lower", and 流 means "flow" or "current", combining to signify the "lower reaches" of a river. Historically in Chinese social and philosophical thought, what is physically lower was often associated with baseness or impurity. This spatial metaphor was then applied to human behavior, where 下流 evolved to describe actions or speech considered morally "low" or degrading, moving from a geographical term to a firmly entrenched pejorative descriptor of unethical and lewd conduct.