在抽象代数及范畴论中，子商是很常用的概念。这是子结构（例如子群、子模、子表示）与商结构（例如商群、商模、商表示）的推广。

固定一个范畴 。若 中的对象 能表成某对象 的子对象之商，则称 为 的子商。在群与阿贝尔范畴的框架下皆可定义子商。在群论中，有时也将子商称为截面。

In the mathematical fields of category theory and abstract algebra, a subquotient is a quotient object of a subobject. Subquotients are particularly important in abelian categories, and in group theory, where they are also known as sections, though this conflicts with a different meaning in category theory.