Nexus Zero is coordinate within the Vok Nebula, the homeland of the alien race known as the Vok. It is located beyond the known regions of space on Cybertronian star charts. The location is called a "Nexus" because it is the central node of a network of interconnected wormholes that allow the Vok to travel quickly between various points in time and space. Likewise Nexus Earth was part of this network as related to the Vok attempt to control and enhance human evolution.
After recieving a signal from the Flying Island, the Vok left Nexus Zero to investigate what was happening on Nexus Earth. Discovering the Maximals and the Predacons, they decided to sterilize the planet, activating the Planet Buster, at which point they returned to Nexus Zero.
The Nexus Earth node of the network was destroyed along with the Metal Hunter Base. Because this, Tigerhawk was sent via a comet-like vessel to deal with the continued interference of the Transformers.
Larry DiTillio originally intended the concept of Nexus Zero, then called the Vok Nebula, as the source and destination of Protoform Transformer sparks. However, this idea was not mentioned in the show and probably cancelled. The idea was later replaced with the Allspark of Primus.