Base Delta Zero (BDZ) is the Imperial code order for an orbital bombardment to completely destroy a world's life, industry, and natural resources. This was carried out by melting the crust of a planet to a depth of several kilometers, enough to even wipe out deep-planet survival shelters and bunkers. Unlike other Imperial military codes, Base Delta Zero was not subject to change, so that there was never any confusion when it was issued.
The exact timetable and degree of devastation of a BDZ operation remain unclear, but the data seems to indicate that a planet subjected to Base Delta Zero operation was devastated to such a degree that terraforming a lifeless planet would take less time and effort than restoring the shattered ecosystem of the target world. Other sources indicate the operation could be conducted in less than a day, and perhaps not more than an hour.