Regions are the names that are given to the different locations that are groups of cities, like a state or so.
There are currently five known main regions Regions in the Pokemon world. Each region has different Pokemon that are native to that region, though some appear in other regions at times. There are other Regions, however, it is unknown where those regions are in comparison to the other regions.
There are also two different groups of Regions that are more or less disconnected. The first group is the four Regions in the 'country' that is referred to as 'Kanto', for lack of an official group name. The other is Unova, and any Regions that are close to this. It has been officially stated that Unova is far away from Kanto and it's bordering regions, even further than Sinnoh and Hoenn were from Johto and Kanto, which Unova shows by having exclusively it's Native Pokemon for the most part.
List of RegionsEdit
These are the different Regions in the Pokemon World