A Zone is an inviolable area with a strong magnetic field said to rip through spacetime acting similar to a wormhole. A certain Zone dubbed Stoker 01 served as an important plot element in Getter Robo Arc.
A zone possesses a strong magnetic field that disrupts most radars and the field can even cause anomalies like severe weather patterns like sudden lightning storms. The magnetic field can also even cause tears in spacetime allowing entire armies to move through them and back.
Many years ago a meteor fell into the Pacific Ocean causing a series of anomalies. A wormhole in space used the signal on earth as a beacon for the Andromeda Country to have their invading force move through them in order to destroy the source of Getter Rays. It was used by the alliance of the Saotome Institute and the Dinosaur Empire to fight against the Andromeda Country to send their Getter robots to destroy the mothership.