This document introduces the concept of the rhombus and how to calculate its area. It defines key terms like base, altitude, and diagonals. It notes that a rhombus is a parallelogram where all four sides are the same length. The properties are that the sides are equal, opposite angles are equal, and opposite sides are parallel. It then explains that the diagonals divide the rhombus into four equal triangles and the area of the rhombus is half the product of the two diagonals.