What is a quadrilateral with four congruent sides called?

A quadrilateral with four congruent sides is known as a rhombus. A rhombus not only has all sides of equal length but also possesses the property that its opposite angles are equal and adjacent angles are supplementary. Additionally, the diagonals of a rhombus bisect each other at right angles, making it a special type of parallelogram.

In contrast, a rectangle, while also a type of parallelogram, has four right angles and opposite sides that are equal, but not necessarily all four sides congruent. A general parallelogram has pairs of opposite sides that are equal and parallel but does not require all four sides to be congruent. A trapezoid is defined as a quadrilateral with at least one pair of parallel sides, and its sides do not need to be congruent. Therefore, the unique characteristics of the rhombus are what make it the correct answer to the question regarding quadrilaterals with four congruent sides.