What defines a similar triangle?

A similar triangle is defined as a triangle that has the same shape as another triangle, which allows for the possibility of differing sizes. This means that corresponding angles in the two triangles are equal, while the lengths of the sides may be proportional rather than identical. The concept of similarity in triangles focuses on the relationships between their angles and sides, rather than their actual dimensions.

While it is true that triangles with the same area or those that are both equilateral might exhibit some form of similarity under specific conditions, those definitions do not universally apply to all similar triangles. Additionally, while congruent angles indeed play a critical role in defining similarity, the complete essence of similar triangles encompasses both angle comparison and side length ratios, as highlighted in the correct answer. Therefore, stating that similar triangles share the same shape—regardless of size—is the most comprehensive and accurate definition.