This document provides definitions and properties related to triangles: - It defines different types of triangles based on sides (equilateral, isosceles, scalene) and angles (acute, right, obtuse). - It identifies key parts of triangles like vertices, adjacent/opposite sides, hypotenuse, legs, and base. - It describes interior and exterior angles and states the Triangle Sum Theorem that the interior angles sum to 180 degrees. - The Exterior Angle Theorem and corollary relating right triangles are also presented.