Phase difference
for two sinusoidal quantities, difference in their initial phase modulo 2 π
Phase difference can be defined as the difference between the position of the two waves propagating in the same direction (in a particular time), they don't rise or fall together. At a particular time, they make a difference in amplitude in their motion. For an example, if we consider two pendulum having same time period, now one is starting oscillating after a while another pendulum sets for oscillating then a phase difference is being established in between them.