Definition of "adjunction"

The act of joining; the thing joined or added.  examples

(law) The joining of personal property owned by one to that owned by another.  examples

(category theory) Given a pair of categories C and D : an anti-parallel pair of functors F : C → D and G : D → C and a natural transformation η : id C → G F called “unit” such that for any object A ∈ C , for any object B ∈ D , and for any morphism f : A → G B , there is a unique morphism g : F A → B such that G g ∘ η A = f . (Note: there is another natural transformation called “counit” as well but its existence may be derived by theorem.) The pair of functors express a similarity between the pair of categories which is weaker than that of an equivalence of categories.  examples