4. A polygon that has congruent sides (equilateral) and congruent angles (equiangular) is said to be a polygon.

A polygon with all sides congruent is equilateral, and one with all angles congruent is equiangular. When a polygon has both properties, it is called a regular polygon. Therefore, “regular” is the correct choice; “similar” describes figures with the same shape, not necessarily a polygon with all sides and angles congruent.

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