While trying to read the following article
Schottenfells, Ida May. Two Non-Isomorphic Simple Groups Of The Same Order 20,160.
I found the term "holoedrically isomorphic". In an abstract for the article, I also came across the claim that "Holoedric isomorphism is the only isomorphism that can exist between two simple groups."
I haven't been able to find a definition for this term anywhere. Presumably it is a stronger notion than that of a normal isomorphism of groups? What does it mean?