Serein (meteorology)

Serein (/sɪˈriːn/; [səʁɛ̃] in French) refers to rain falling from a cloudless sky. This sort of rain is said to take on the form of a fine, light drizzle, typically after dusk. The name derives from French serein, meaning "serene", or "clear" (as in unclouded). An alternative etymology is from Old French serain, evening.

An explanation could be the evaporation of the cloud droplets when precipitation drops are formed. Anyway, for others the phenomenon is simply non existing and should be considered equivalent to rain falling from a distant cloud, when there is a strong vertical wind shear between the cloud itself and ground, while the sky is apparently clear.