In the general equation , we only considered sinusoids starting at 0,0. But this isn't always the case. Sinusoids can be shifted right or left.

A waveform may lead or lag as a result. This lead or lag is denoted by and is called the phase angle, the difference in angle that causes two saves to be in lead or lag(out of phase).

Again, when two waves are leading or lagging each other, they have a phase difference. They are out of phase.

Now that we know the concept of phase angle, we modify the general equation for an AC sinusoidal voltage as
The difference between phase angles of 2 sinusoids is called the phase difference.