A polygon is said to be a regular polygon if ___.
all its sides and angles are equal
If in a polygon, all the sides and angles are equal, only then is it known as a regular polygon.
Examples: equilateral triangle (regular triangle), square (regular quadrilateral), regular hexagon, etc.
A rectangle has all its angles equal and a rhombus has all its sides equal, but still are not regular polygons, as a rectangle has unequal adjacent sides and a rhombus has unequal adjacent angles.