What type of triangle has all sides of different lengths?

A triangle with all sides of different lengths is classified as a scalene triangle. In this type of triangle, not only do all three sides differ in length, but the angles also vary, ensuring that no two sides or angles are the same. This distinguishes scalene triangles from other types, such as equilateral triangles, where all sides and angles are equal, and isosceles triangles, which have at least two sides of the same length. Right triangles, on the other hand, are defined by having one angle that measures 90 degrees, but can fall into either the scalene or isosceles categories depending on the lengths of their sides. Thus, the defining characteristic of a scalene triangle is the uniqueness of its side lengths, making this classification the correct answer.