What defines a triangle?

A triangle is defined as a three-sided figure, which means it consists of three edges and three vertices. This definition encompasses the essential characteristics that identify a triangle and distinguishes it from other geometric shapes. Every triangle is formed by connecting three points, known as vertices, with straight line segments known as sides. The arrangement of these sides also gives rise to three interior angles, which, when summed, equal 180 degrees. This angle sum property is specific to triangles and differentiates them from quadrilaterals, which have an angle sum of 360 degrees. The mention of three-dimensional shapes is not applicable to triangles, as they are inherently two-dimensional figures. Therefore, the defining feature of being a three-sided figure accurately encapsulates what a triangle is.