In geometry, a number of tests for congruence and similarity involve comparing corresponding sides. In such tests, each side in one figure is paired with a side in the second figure, taking care to preserve the order of adjacency - in other words, if side A in figure #1 is adjacent to sides B and C, and its pair in figure #2 is side X which is adjacent to sides Y and Z, then B and C must be paired with Y and Z in either order. The pairs of sides are then known as corresponding sides.Typically, congruency tests look for pairs of corresponding sides to be equal in length, and similarity tests look at whether the ratios of the lengths of each pair of corresponding sides are equal.en.wikipedia.org