Fur，皮毛，是一个不可数名词，例如My dog has thick fur on its body，我的狗狗身上有厚厚的皮毛

但是当指动物毛的根属实，这又是一个可数名词，例如，there is a fur on your coat的外套上有一根毛毛，累似的还有hair，这个词，We have long hair，There is a white hair