This occurs when it is milked and then left for a while until some milk descends, then it is milked again; so the interval between the two milkings is the fuwaq. Thus, the term fuwaq was metaphorically applied in the context of waiting.
وَذَلِكَ أَن تُحلَب وتترك سَاعَة؛ حَتَّى ينزل شَيْء من اللَّبن , ثمَّ تحلب فَمَا بَين الحلبتين فُواق؛ فاستُعير الفُواق فِي مَوضِع الِانْتِظَار.
