E.V. = eingetragener Verein = registered club.
What HSV are doing is spinning off their professional teams into a separated stock company (= "Aktiengesellschaft", A.G.), meaning their professional football team that we know as HSV stops being part of HSV e.V. and is now HSV A.G. Means more financial profit, but there's also the risk of a Leverkusen or Hoffenheim scenario, i.e. HSV turning into a plastic club.