A category **C** must have zero morphisms for the concept of normality to make complete sense.
In that case, we say that a monomorphism is *normal* if it is the kernel of some morphism, and an epimorphism is *normal* (or *conormal*) if it is the cokernel of some morphism.

**C** itself is *normal* if every monomorphism is normal.
**C** is *conormal* if every epimorphism is normal.
Finally, **C** is *binormal* if it's both normal and conormal.
But note that some authors will use only the word "normal" to indicate that **C** is actually binormal.

Suppose that *G* is a group and *H* is a subgroup of *G*.
Then the inclusion map *i* from *H* to *G* is a monomorphism.
*i* will be normal if and only if *H* is a normal subgroup of *G*.
(In fact, this is the origin of the term "normal" for monomorphisms.)
On the other hand, every epimorphism in the category of groups is normal (since it is the cokernel of its own kernel), so this category is conormal.

In an abelian category, every monomorphism is the kernel of its cokernel, and every epimorphism is the cokernel of its kernel. Thus, abelian categories are always binormal. The category of abelian groups is the fundamental example of an abelian category, and accordingly every subgroup of an abelian group is a normal subgroup.