Operational Security. The act of keeping information, fleet movements, fittings, etc. concealed to prevent the enemy from getting your location, fleet composition, battle plans, etc. In practice, this means compartmentalizing information. Logistics pilots don't need to know the overarching battle plan, Electronic warfare specialists don't need to know how far ahead your scouts are, logistics pilots only needs to know where they're staging to, not the full fleet location. The idea being to minimize how much your enemy knows about you. To the average pilot, this means not talking about fleets, not using local chat, not talking about doctrines on forums or trying to "show how important they are" by revealing classified information, and not talking about the goals of ops anywhere where spies could observer.