Common Core Math Vocabulary

Angle - Definition with Examples

What is an Angle?

Angle Definition: An angle is formed by joining two rays meeting at a common end point.

Angle Definition

Angle Symbol:

An angle is represented by a symbol 

∠AOB is read as angle AOB.


Angles Around Us

Angles can be found in food items, between the hands of a clock, in photo frames, etc.

angle around us


Parts of an Angle

Parts of Angle

Arms of an angle: The two rays that are joined to form an angle are called the arms of an angle. In the picture, OA and OB are the arms of an angle.

Vertex of an angle: The common point where the two rays meet to form an angle is called the vertex. The point O in the picture is called the vertex.


Naming an Angle:

Naming an angle

In geometry, an angle is named either by:

  • its vertex: ∠A

  • a number on its vertex: ∠1

  • the three points on the angle, in which the vertex goes in the center: ∠BAC or ∠CAB



Measuring an Angle

Angles are measured in degrees and radians.

A full circle is equal to 360 degrees, which corresponds to one complete rotation.

Measuring angle using clock


The degree is represented with the help of a small circle used as a superscript, placed on the right-hand side of the number.

For example, 90° means 90 degrees.


Types of Angles

Classifying angles on the basis of their measurements:

Acute Angle

Acute Angle

An angle which measures more than 0° but less than 90° is called an acute angle.

Right Angle

Right Angle

An angle which measures exactly 90° is called a right angle.

Zero Angle

Zero Angle

An angle which measures exactly 0° is called a zero angle.

Obtuse Angle

Obtuse Angle

An angle which measures more than 90° but less than 180° is called an obtuse angle.

Complete Angle

Complete Angle

An angle which measures exactly 360° is called a complete angle.

Straight Angle

Straight Angle

An angle which measures exactly 180° is called a straight angle.


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