In this video you will learn about the topics basic terms and definitions of the chapter lines and angles.

**Collinear Points:**Three or more points are said to be collinear, if a line passes through all three points.**Ray:**Ray is a part of line, which has one the end point and can be extended indefinitely on the other end.- When two rays have a common initial point they are said to have formed an angle.
- The angle is measured in degrees or radians.
**Acute angle:**If the measure of an angle lies between 0^{o}and 90^{o}.**Right angle:**If the measure of an angle is equal to 90^{o}.**Obtuse Angle:**If the measure of an angle lies between 90^{o}and 180^{o}.**Straight angle:**If the measure of an angle is equal to 180^{o}.**Reflex angle:**If the measure of an angle is greater than 180^{o}but less than 360^{o}.

**CBSE Class 9: Heron’s Formula - Applications of Heron’s Formula**

**CBSE Class 9: Lines and Angles - Types of Angles**