The term "Region" refers to the areas on the World Map that can be the target of Liberate and Conquer Missions when playing Chronicle X in Conquest Mode.
World Map
The "World Map", also known as the "Global Operation Map", is a game board mainly used in Conquest Mode to keep track of which Regions someone has or hasn't taken control over, which also has the Conquest Tracker for both sides.
The World Map also contains the Alien Unit Tracker, which can be used in both Game Modes.