Homeset

https://en.wikipedia.org/wiki/Hom-set

In a category 𝒞, the collection of all morphisms between two objects A to B, is the hom-set between A and B, is most often denoted by Hom(A,B).

Other notations: Homᶜ(A,B), Arrᶜ(A,B), Arr(A,B), 𝒞(A,B).

The term hom-set is a misnomer because the collection of morphisms is not required to be a set. A category where Hom(A,B) is indeed a set, for all objects A and B, is called locally small.

The domain and codomain are in fact part of the definition of morphisms. For example, in the category of sets, where morphisms are functions, two functions may be identical in terms of the sets of ordered pairs - they may have the same range, while having different codomains. However, from the viewpoint of category theory, such functions are different. Therefore, many authors require that the hom-classes Hom(A,B) be disjoint (set/class/collection). In practice, this is not a problem because if the disjointness does not hold, it can be assured by appending the domain and codomain, e.g. as (Hom(A,B), A, B) such that an ordered triple represents homset of morphisms.