What is meant by phase angle?

Hint: Here, we have to understand the meaning of the term phase angle. In basic Physics, phase angle is used in terms of firstly, wave motion and secondly, for describing alternating current and voltage. We will discuss in terms of both the concepts. Basically, it represents angular shifts or displacements corresponding to two points having the same value along the y-axis.

Complete step by step solution:
Graphically understanding, phase angle is the angular displacement of a point on a sinusoidal wave from a reference point or time. Both waves and alternating quantities are expressed in the form of waves. So, the term is used in both ways.
In electrical quantities, alternating current as voltage are expressed as sinusoids. In waves, amplitude, velocity and acceleration of particles have alternating values and hence are expressed as sinusoids.
In an electrical circuit, we can recognize angle between resistive current and total current on phasor diagram as current phase angle(Φ)
 

The difference in two quantities have the same frequency and two corresponding points attain maximum value or zero value at two different instants, then the angle between two alternating quantities is called difference of phase angles. Below is the explanation of phase angle in terms of waves.

 ΔΦ represents phase difference
For the purple graph, ΔΦ is the phase angle.

Note: Phase angle for any quantitative angle can be defined as the angle at the instant at which it attains zero value measured taking origin as reference. It can also be defined as the angle between total current and resistive current in an electrical circuit. If the phase angle in any phasor diagram is counter clockwise, it is taken as positive and negative for clockwise direction.