Portion of a
plane bounded by a closed simple curve called the
boundary of the region.
A closed curve divides the plane into two regions: an
interior region formed by the points located inside the closed curve and an
exterior region formed by the points located outside the closed curve.
![](https://media.scolab.com/Illustrations/Lexique/Interior_Exterior_Regions.svg)
There can be as many regions as there are simple curves.
![region](https://media.scolab.com/Illustrations/Lexique/v5%20-%202/region_en.svg)