Some theory is tuple of set of axioms (including ones that are statements about data), set of inference rules and set of already deduced theorems (statements) in it. Theory can be discovered by human being by lengthy and partially informal process. But theory can also be learned by neural networks. There are true but unknown theories and there are known theories that approximate the unknown ones to some degrees. There is reasoning with degrees of truth.
My question is - is there some philosophical, epistemic, gnoseological know that measures how much one theory is close to another theory, some kind of distance among theories? Of course, different aspects can be measured (complexity, expressivity, number of statements with the same truth value of both theories) and that is why different measures can exist. I am not seeking the ultimate list of such aspects and measures. I am just seeking the common name, term, keyword that is used in the philosophy to describe the efforts to research the closeness of theories.