subobject

Noun

 * 1) An object that is part of another object.
 * 2)  An object and a monomorphism from it to another object, which monomorphism is interpreted as an inclusion. Actually it is an equivalence class of monomorphisms to the same object, where the equivalence relation is the ability of a pair of monomorphisms to factor through each other.

Derived terms

 * subobject classifier