How is a quotient defined in an abelian category?

Question

In CWM Saunder Maclane, exercises $6$ page $202$ states:

For sub-object $u \leq v$ of an object $a$ in an abelian category, define a "quotient" object $v/$u.

What is the exact definition of $v/u$ in this situation?

Answer 1

$v/u$ is the cokernel of the monomorphism $u \to v$ (which exists because of $u \leq v$).