Here, you will come across definitions and basic terms related to a line segment, collinear points, intersecting lines, ray, non collinear points and non intersecting lines. You shall also know about various pairs of angles such as linear pair of angles, the reflex angle, vertical opposite angle, complementary angle, adjacent angle and supplementary angles.The chapter also gives you an idea of transversal and parallel lines with the help of the theorems to support over it. Here, the chapter also focuses upon of angle sum property of a triangle.