A continuous set of points on a plane that can be drawn without lifting your pencil.
The main types of curved lines are:
![](https://media.scolab.com/Illustrations/Math%20Objects/Line_types_all.svg)
A simple closed curved line defines two regions on a plane so that it is impossible to pass from one to the other without crossing the line called the boundary of these regions.
A polygon, such as the decagon below, is a simple closed curved line:
![décagone_quelconque](https://media.scolab.com/Illustrations/Lexique/deformed_decagon.svg)