What are polygons and quadrilaterals?

Answer 1

A polygon is any figure that can be subdivided into triangles, which means that it has to have straight sides. A quadrilateral has straight sides, but exactly four of them. Squares, rectangles, parallelograms are all quadrilaterals and polygons.
A polygon has 3 or more sides whereas quadrilaterals are 4 sided polygons

Answer 2

A polygon is a closed plane shape that is bounded by straight sides. A polygon can have three or more sides - up to infinitely many of them. A quadrilateral is a polygon with four sides.