Angles can exist anywhere in the coordinate plane where two rays
share a common vertex. If this vertex is at the origin of the plane and
the initial side lies along the positive $x$-axis, then the angle is said to be in standard position. Some angles in standard position are shown
below.

Angles in standard position can be classified according to the quadrant
contains their terminal sides. For example, an angle whose terminal side
lies in the first quadrant is called a first quadrant angle. If the
terminal side of an angle lies along one of the axes, then that angle doesn't
lie in one specific quadrant; it lies along the border of two quadrants. Such
angles are called a quadrantal angle.