What is a Phase?

A phase can be defined as the position of a point at a instant of time on a waveform cycle. Phase can also be expressed as the relative displacement between two or more waves having similar frequency. A complete cycle of a waveform is 360° of phase as shown in figure below

A wave of certain frequency that is occurred before or ahead of another wave of same frequency is called a leading phase. A wave that is occurred after or behind another wave of same frequency is called a lagging phase.