Regions are a game mechanic in Agar.io. When the game starts, the player will have a menu, the player can then click the gear button and change multiple mechanics. One being the Region of the server. There are 9 regions the player can select: North America, South America, Europe, Russia, Turkey, East Asia, China, and Oceania.
The most crowded of all servers is Europe, second North America, the least crowded is China, and the second least crowded being Oceania. But China is the region with a big clan called [TW] as in [Taiwan].