The "Ringo Zone" is where Ringo zapped Garnet, Hoppy, and Hopper by using the sacred magic gem of ultimate power in the episode "Garnet's Universe". It is a vast place covered with green and blue colored rings and swirls. It's a part of Steven's imaginary story about Garnet's activities.
Ringo brings Garnet, Hoppy, and Hopper to the Ringo Zone because it is there that his powers are the strongest. Garnet was forced to fight Ringo, and after she defeated him he was trapped in the Ringo Zone, forever.
- It may be a reference to the Phantom Zone from the Superman comics.