When we talk about Feynman diagrams we know they are tools to make calculations easier and more intuitive. Moreover, it's said that they are "topological" representations of the interactions.
But, what does it mean that they are topological objects? Topolgy is a brach of Mathematics that deals with spaces where you can define distances, limits, norms..., i.e., where you can define a notion of distance between its their elements. Nevertheless, I don't see how this is related to the diagrams.