The library divides novels into major genres and further organizes them into subcategories for more specific classification.

subcategories 是由前缀 sub-（表示"在...之下"或"次要的"）和名词 categories（类别）组成的复合名词。sub-表示"次级"的意思，所以 subcategories 指的是"子类别"或"次级分类"，即在主要分类下更细分的类别。