A triangle is a three-sided polygon characterized by its three edges and three vertices. The sum of the interior angles in a triangle always equals 180 degrees. Triangles can be classified into different types based on their angles: acute, right, and obtuse. They can also be categorized by their sides as equilateral, isosceles, and scalene. Triangles are fundamental shapes in geometry and are widely used in various fields, including architecture and engineering. The properties of triangles make them essential in constructing stable structures, as they distribute weight evenly. Additionally, the Pythagorean theorem applies specifically to right triangles, providing a method to calculate the lengths of their sides.