A subregion is a smaller part of a larger region, like a piece of a puzzle.
Subregion is a way to talk about smaller areas inside a bigger area, like a state inside a country.
Examples:
The desert is a subregion of the continent.
The forest is a subregion of the park.
The subregion has many trees and animals.
The big region is like a pizza, and the subregions are like slices of the pizza.
In the land of ice and snow, there is a subregion where it's always warm.
The subregion is like a small town inside a big city.