In geometry, what is the term for a polygon with three sides?

A polygon with three sides is called a triangle. This term derives from the Greek words "tri" meaning three and "angle," referring to the three angles formed by the intersection of its three sides. Triangles are fundamental shapes in geometry and have various properties such as the sum of the interior angles always being 180 degrees. Additionally, triangles can be categorized into different types based on their side lengths (equilateral, isosceles, and scalene) and their angles (acute, right, and obtuse). Understanding the characteristics of triangles is essential as they serve as building blocks for more complex geometric concepts.