If I remember correctly for those who don’t know, a base Delta Zero operation is total destruction of all civilizations on the planetary surface through a massive orbital bombardment.
Indeed. The paragraph from The Imperial Sourcebook states that "If Army commanders deem the surface situation to be beyond hope of victory, or if the proper political authorities directly command it, the Navy is to execute a series of punitive attacks upon the target. The attacks are given code names which vary according to the mission and change frequently. The only code name which has not yet changed is "Base Delta Zero", the code for complete destruction of all "assets of production", including factories, arable land, mines, fisheries, and all sentient beings and Droids. The code name has not yet changed so there can be no possibility of confusion when a Base Delta Zero is ordered."
Army mercenary units like the First Sun Mobile Regiment perform the same order on land, but for warships BDZ usually means to destroy the entire surface and subsurface structures of the planet they’re targeting.