Question

what do you mean by phase and phase difference​

Answer 1

In sinusoidal functions or in waves, "phase" has two different, but closely related, meanings. One is the initial angle of a sinusoidal function at its origin and is sometimes called phase offset or phase difference. Another usage is the fraction of the wave cycle that has elapsed relative to the origin.

Answer 2

Phase is generally said for functions that repeat itself most commonly in SHM.

Here, phase is measured in angles. The angle with respect to mean position at time t=0 (time in which an object starts SHM) is called phase.

For example, we usually study SHM of a body represented as sinusoidal wave, where body starts SHM from mean position. In sine wave it is at x=0 at t=0. So phase is 0°

Phase difference is difference in phase between two bodies executing SHM.