What is the name given to a triangle that has different lengths for all its sides?

A triangle with different lengths for all its sides is called a scalene triangle. In a scalene triangle, not only are all three sides of different lengths, but all three angles are also different. This distinction sets scalene triangles apart from other types.

For example, an isosceles triangle has at least two sides of equal length and consequently two equal angles. An equilateral triangle has all three sides of the same length and therefore all three angles are equal, each measuring 60 degrees. An acute triangle is defined by its angles; it has all angles measuring less than 90 degrees, but it can be scalene, isosceles, or equilateral in terms of side lengths.

Thus, the term "scalene" specifically highlights that all sides are unequal, which is why this term is the accurate descriptor for the triangle in question.