Basic terminology

If a given ray OA (written as ) rotates around a point O from its initial position to a new position, it forms an angle θ as shown below.

(initial position) is called the initial side of θ.

(terminal position) is called the terminal side of θ.

The angle formed by a ray rotating anticlockwise is taken to be a positive angle.

An angle formed by a ray rotating clockwise is taken to be a negative angle.