Which of the following is a property of an isosceles triangle?

An isosceles triangle is defined by having at least two sides that are equal in length. This characteristic leads to several specific properties, such as the angles opposite those equal sides also being equal. When two sides of a triangle are the same length, it forms an isosceles triangle, making it distinct from other types of triangles.

In contrast, the option indicating that all sides are equal describes an equilateral triangle, which is a special case of an isosceles triangle but does not define it. The statement about all angles being equal is also specific to equilateral triangles, as equilateral triangles have three equal sides and three equal angles. Finally, the option stating that no sides are equal defines a scalene triangle, which is not at all relevant to the properties of an isosceles triangle. Thus, identifying that an isosceles triangle is characterized by having two equal sides clearly establishes why that is the correct choice.