what is phase difference and how to visualize it? i am able to understand it pretty well in sinusoidal waves but please tell me what it is in other type of waves like plane waves,spherical waves,etc.
Edit: I think you'll find all the details you need at this question.
As Asher commented, when a wave is described as sinusoidal, or triangular, or square, that's its amplitude profile. When a wave is described as plane or spherical, that's the spatial profile perpendicular to the direction of propagation. For example, a plane wave of sinusoidal amplitude will have the same phase, i.e. amplitude at all $(x,y)$ coordinates for a given $z$ (direction of propagation). If the amplitude is maximum at $z_0$, then the amplitude will be a peak at $z_1$ which is one-quarter wavelength away.
Similarly, for a spherical wave, the phase is the same on all points on a spherical surface (common radius from the origin).