Regular Polygons
A Regular Polygon has
all side equal
all angles equal
Examples :
In ∆ ABC
AB = AC = BC
and ∠A = ∠B = ∠ C
Irregular polygons
A Polygon which is not a regular Polygon is an irregular polygon.
Examples :
Δ ABC is a right angle triangle,
where ∠A ≠ ∠B ≠ ∠C
and AB ≠ BC ≠ AC.
∴ Δ ABC is a regular polygon
ABCD is a square in which
AB = BC = CD = DA
and ∠A = ∠B = ∠C = ∠D
∴ ABCD is a regular Polygon
∴ Δ ABC is not a regular polygon
ABCD is a rectangle,
In a rectangle, all angles are 90°
⇒ ∠A = ∠B = ∠C = ∠D
And opposite sides are equal
∴ AB = CD and AD = BC
But, AB ≠ BC ≠ CD ≠ AD.
i.e. All sides are not equal
∴ ABCD is not a regular Polygon

Davneet Singh is a graduate from Indian Institute of Technology, Kanpur. He has been teaching from the past 8 years. He provides courses for Maths and Science at Teachoo. You can check his NCERT Solutions from Class 6 to 12.