The document discusses different types of quadrilaterals: - Parallelograms have both pairs of opposite sides parallel. - Rhombuses have four equal sides. - Rectangles have four right angles. - Squares are both rhombuses and rectangles, with four equal sides and four right angles. Theorems state that a quadrilateral is a rhombus if its diagonals are perpendicular, or if each diagonal bisects a pair of opposite sides. A quadrilateral is a rectangle if its diagonals are parallel.