Four-sided figures are often referred to as quadrilaterals. Quadrilaterals have four sides and four angles. The four sides can be equal in length, making the quadrilateral a square. When the opposite sides are parallel, it is called a parallelogram. If the parallelogram is also a rectangle (with 90-degree angles), it is a rectangle. If the angles are not equal, it is a trapezoid. Finally, a rhombus is a quadrilateral where all four sides are equal in length. Each of these synonyms describes a specific type of four-sided figure, and it is essential to understand their differences.