Wave speed refers to how fast a point on a wave moves, which can be understood in terms of phase velocity and group velocity. The discussion highlights the importance of distinguishing between these concepts, as well as the movement of points on transverse versus longitudinal waves. Understanding wave speed is crucial for grasping interference and path difference, which are related to wavelengths. The formulas for path difference, including path difference = nλ and path difference = (n + 1/2)λ, are essential for analyzing wave interactions. Further reading and resources are encouraged for deeper comprehension.