A geometric shape with three sides is called a triangle. Triangles are one of the simplest and most fundamental shapes in geometry, characterized by three edges and three vertices. They can be classified into various types based on their angle measurements or side lengths, such as equilateral (all sides equal), isosceles (two sides equal), and scalene (all sides different). The study of triangles also leads to the development of various mathematical principles, including the Pythagorean theorem and trigonometric functions. Triangles are widely used in architecture, engineering, and various fields of design due to their structural stability.