Which type of triangle has at least two sides that are the same length?

A triangle that has at least two sides that are the same length is defined as an isosceles triangle. In an isosceles triangle, the two sides that are of equal length are often referred to as the legs, and the angle between them is called the vertex angle. The triangle also has two equal angles opposite the equal sides, which is a defining characteristic of this triangle type.

In contrast, an equilateral triangle has all three sides of equal length, which is a specific case of the isosceles triangle because it also meets the criterion of having at least two sides that are the same length. However, the defining characteristic of an isosceles triangle is not dependent on all three sides being equal, making it distinct.

A scalene triangle, on the other hand, has all sides of different lengths, and thus does not meet the criteria at all. An acute triangle refers to the type of angles within the triangle, specifically one where all angles are less than 90 degrees, and does not address side lengths.

Therefore, the isosceles triangle is the appropriate classification for a triangle that has at least two sides of the same length.