A triangle is a three-sided polygon that is one of the simplest shapes in geometry. It consists of three straight edges and three vertices, where the edges meet. The sum of the interior angles of a triangle is always 180 degrees. Triangles can be classified into different types based on their sides and angles, such as equilateral, isosceles, and scalene triangles. Triangles are also categorized by their angles: acute triangles have all angles less than 90 degrees, right triangles have one angle equal to 90 degrees, and obtuse triangles have one angle greater than 90 degrees. Triangles are fundamental in various fields, including architecture, engineering, and art, due to their structural stability and aesthetic appeal.