The lines of symmetry in a rhombus are located along its diagonals.

A rhombus is a specific type of quadrilateral characterized by having all four sides of equal length. One of the defining properties of a rhombus is that its diagonals bisect each other at right angles (i.e., at $90^\circ$). This property implies that each diagonal divides the rhombus into two congruent triangles. Consequently, the diagonals serve as lines of symmetry.

To identify the lines of symmetry, simply draw the diagonals extending from one vertex to the opposite vertex. These diagonals will intersect at the center of the rhombus, thereby partitioning it into four right-angled triangles. Each diagonal functions as a mirror line, reflecting one half of the rhombus onto the other. Thus, a rhombus possesses exactly two lines of symmetry, which correspond to its diagonals.

Grasping this concept is essential for tackling problems associated with symmetry, area, and other geometric attributes of rhombuses. When the diagonals are drawn, it becomes evident that they divide the rhombus into four equal sections, which can be valuable for various calculations and proofs in geometry.