DECAGON
A four-sided polygon with opposite sides parallel and all sides congruent is a square.
A four-sided polygon with all sides congruent and with four right angles is a square.
octagon
A four-sided polygon with all sides parallel and congruent is a rhombus. If all the angles are equal, it is a special case of a rhombus called a square.
It is a regular octagon.
It is a regular 5 sided pentagon
A rhombus is a quadrilateral with four equal sides
It can be many types of polygons a square is an easy one, but there are also equallateral triangles when all the sides of a triangle are congruent with each other. There is also an octagon an 8 sided polygon that can be congruent sides, and it just keeps going on.
an equilateral triangle
An irregular octagon.
A square or a rhombus
It all depends on what kind of polygon it is. It may have no congruent sides or all congruent sides.