What does the term 'speed' in wave properties refer to?

The term 'speed' in wave properties refers to the distance that a wave travels per unit of time. In this context, choice B is close to the concept since it discusses the horizontal motion of a wave. However, to be precise, the speed of a wave is indeed defined by how quickly a given point on the wave, such as a crest or trough, moves through space.

In wave physics, speed is typically calculated using the formula: wave speed = wavelength × frequency. The correct understanding centers on how fast the entire wave travels through the medium, which can be categorized as the overall movement of the wave rather than just a point on it. Therefore, speed refers to the propagation rate of the wave, indicating that the location of a crest or trough is moving horizontally across a distance over time.

Other options present concepts related to wave behavior but do not accurately define 'speed.' For instance, time taken by a wave to pass a point would describe a duration rather than motion, while frequency multiplied by amplitude does not yield speed—and the distance between adjacent crests describes wavelength, not speed. Thus, focusing on the overall propagation of the wave clarifies the correct interpretation of speed in this context.