A triangle with all three sides of different lengths is called a "scalene triangle." In a scalene triangle, not only are the side lengths unequal, but the internal angles are also different. This distinguishes scalene triangles from equilateral triangles, where all sides are equal and all angles are the same, and isosceles triangles, where two sides are equal. Scalene triangles can vary significantly in appearance and proportions, making them an interesting study in geometry and trigonometry.