A polygon is a closed figure made up of line segments.
A simple polygon has only one boundary, and it doesn't cross over itself. The sides of a simple polygon do not intersect.
Complex polygon is a polygon whose sides cross over each other one or more times.
Let's go through some examples.
Is this polygon simple or complex?
In the given polygon the lines do not intersect each other at any point.
So, it is a simple polygon.
Is this polygon simple or complex?
In the given polygon five lines intersect each other.
So, it is a complex polygon.