A pushout of two morphisms 
and 
in a category is an object
with morphisms 
and 
satisfying 
and the following universal
property: every pair of morphisms 
and 
with 
factors uniquely through a morphism 
.
In the category of sets, a pushout is obtained from the disjoint union of 
and 
by identifying 
with 
for every 
. A pushout is the categorical dual of a pullback.
