Straight angle if the initial and final positions of a rotating ray are opposite to each other (on the same line)the angle formed is called a straight angle.

Zero angle if the initial and final positions of a ray coincide without making any revolution we say that the angle formed is zero angle.

Angle between y axis and a straight line

Right angle if the initial position of the ray OA is horizontal and it rotates to occupy vertical position OB then we say that the angle formed is a right angle.

The measure of a straight angle is

Straight Angle and Reflex Angle

Complete angle if a rotating ray after making a complete revolution coincide with the initial position the angle formed is called a complete angle.

Angle as rotation of a ray.