What type of polygon has all sides congruent but not necessarily all angles equal?

The correct answer is that the type of polygon with all sides congruent but not necessarily all angles equal is known as an equilateral polygon. This term specifically refers to shapes where all sides have the same length, but it does not impose any restrictions on the measures of the angles.

In contrast, a regular polygon is defined by having both all sides congruent and all angles equal, which does not match the criteria presented in the question. An irregular polygon lacks any uniform properties in either its side lengths or angle measures, making it distinct from the focus on side lengths in this case. Lastly, an equiangular polygon is characterized by having all angles equal but does not ensure that the sides are of equal length, which is also not applicable here. The concept of equilateral polygons is significant in geometry as it highlights a key property of side lengths while allowing for variation in angles, distinguishing it from other types of polygons.