The product of a family of objects of a category
is an object
,
together with a family of morphisms
such that for
every object
and every family of morphisms
there is a unique morphism
such that
for all .
The product is unique up to isomorphisms.
In the category of sets, the product is the Cartesian product, and in the
category of groups it is the
group direct product. In both cases, , and
is the projection onto the
th factor.