The bottom number in a fraction; the number that denotes the parts into which the whole is divided (pairs with the numerator). It cannot be zero.
この分数は分母が4で、分子が1です。
This fraction has denominator 4 and numerator 1.
分母をそろえて分数の足し算をします。
Make the denominators the same and then add the fractions.
分母が0だと、その分数は定義されません。
If the denominator is 0, the fraction is undefined.