An angle is a combination of two rays (half-lines) with a common endpoint.
The latter is known as the vertex of the angle and the rays as the sides, sometimes as the legs and sometimes the arms of the angle.
We use numerical measurement called degree to measure angles. We use the notation a˚to denote a degrees. The rays OA and OB are called the sides of the angle and O is called the vertex if the angle. The angle subtended by the rays OA and OB is denoted by ∠AOB.
An instrument used to measure the angles is called protractor.