complex fraction
noun [ C ] mathematics specialized uk/ˌkɒm.pleks ˈfræk.ʃən/ us/ˌkɑːm.pleks ˈfræk.ʃən/ (also compound fraction)
繁分数，繁分式
a fraction in which either the numerator (= the number above the line) or the denominator (= the number below the line) is itself a fraction