This document defines and compares rhombuses, rectangles, and squares. It states that a rhombus is a parallelogram with four congruent sides, a rectangle is a parallelogram with four right angles, and a square is a parallelogram that is both a rhombus and a rectangle. The document also presents properties and relationships between these shapes, such as diagonals and angles, and provides theorems about identifying shapes based on their diagonals.