Which triangle has two sides that are equal in length?

An isosceles triangle is defined by having at least two sides that are of equal length. This characteristic is fundamental to the definition of isosceles triangles, distinguishing them from other types. In an isosceles triangle, the two equal sides are often referred to as the legs, while the third side is known as the base. The angles opposite the equal sides are also equal, which provides further properties related to isosceles triangles.

In contrast, a scalene triangle has no sides that are equal, meaning all three sides are of different lengths. An obtuse triangle has one angle that is greater than 90 degrees, but it can have sides of equal length as well; however, it does not inherently define them as equal. An equilateral triangle, while also having equal sides, is a specific type where all three sides are equal in length, which is more restrictive than just having two equal sides. Therefore, the classification of a triangle with specifically two equal sides points directly to the isosceles triangle.