Definition of "pullback"
pullback
noun
plural pullbacks
(category theory) Within a Cartesian square (which has a pair of divergent morphisms and a pair of convergent morphisms) the divergent morphism which is directly opposite to a given one of the convergent morphisms, said to be “along” the convergent morphism which is between that pair of opposite morphisms. (The pullback is said to be “of” the given morphism.)