The unofficial (later semi-official) name given to the city that was once Nos Astra.
Nos Astra, the planetary capital of Illium, was evacuated during the Reaper War, and fell to the machine invaders. Most of the fleeing population crowded into Nos Varda, a neighbouring settlement, which became the seat of government and withstood siege by Reaper forces. When the war concluded, Nos Astra was deemed unsuitable for immediate re-habitation. Therefore, Nos Varda was made the new permanent capital. To maintain a sense of continuity, however, the Illium Board of Governors renamed Nos Varda "Nos Astra".
Therefore, post-Reaper War, most people referring to Nos Astra are talking about NewNos Astra -- that is, the old Nos Varda. The original Nos Astra (or Old Nos Astra) was meanwhile being slowly rebuilt by various corporate interests. Chief among these was media conglomerate the Dwick Dwickcast Syndykyt, based out of One Dwickcast Tower. So influential was the DDS, that the city taking shape from the ruins of Old Nos Astra was often referred to as "Nos Dwicka", and the name stuck.
It seems more complicated than it is. ;)