What type of triangle has all sides equal in length?

A triangle that has all sides equal in length is classified as an equilateral triangle. This type of triangle is characterized by having three equal sides and three equal angles, each measuring 60 degrees. The symmetry inherent in an equilateral triangle means that all sides and angles are congruent, which distinguishes it from other triangle types.

In contrast, an isosceles triangle has at least two sides that are equal in length but does not necessarily have all three sides equal. A scalene triangle, on the other hand, has all sides of different lengths, leading to all angles also being different. Lastly, an obtuse triangle is defined by having one angle that is greater than 90 degrees, which does not provide information about the equality of the sides. Therefore, the defining feature of equal side lengths in the equilateral triangle makes it the correct answer.