A polygon is a flat, 2D shape.
It has straight sides and is fully closed, meaning that all the sides are straight and joined up.
Polygons can have any number of sides.
A regular polygon has all sides of the same length and all angles the same.
For example, an equilateral triangle is a regular polygon - all of its sides and angles are the same.
An irregular polygon is a shape with sides and/or angles at differing lengths and sizes.
A scalene triangle has differing angles and sides.
Let's look at some more polygons in the questions.