This document discusses the key properties and types of triangles. It defines what a triangle is, noting that it has 3 sides, 3 angles, and 3 vertices. It then describes the different shapes of triangles including scalene, equilateral, and isosceles triangles. The document also outlines the different types of triangles based on angle measures, including acute, right, and obtuse triangles. Finally, it provides formulas for calculating the area of a triangle.