Geometric figures, that have the same shape but may not have the same size, are said to be similar figures. Any two congruent figures are always similar but two similar figures need not necessarily be congruent.
Two triangles which have the three angles of one triangle equal to the three angles of the other triangle respectively and the size of their corresponding sides are proportional, are said to be similar triangles.
In other words, two triangles will be similar if:
i. Their corresponding angles are equal.
ii. Their corresponding sides are proportional.