What does amplitude refer to in a wave?

Amplitude specifically refers to the maximum displacement of points on a wave, which can be understood as the height of a crest or the depth of a trough relative to the wave's equilibrium position. In other words, it measures how far the wave stretches from its rest position. A larger amplitude indicates a more intense wave, whether in terms of sound (louder sounds correspond to greater amplitudes) or light (brighter light corresponds to greater amplitudes).

The other concepts mentioned, such as speed and frequency, relate to different characteristics of waves. Speed refers to how fast a wave propagates through a medium, while frequency denotes the number of wave cycles that pass a given point in a unit of time. The point of lowest energy does not accurately define amplitude; instead, it would pertain to the trough of a wave, which is only part of the broader definition of amplitude. Therefore, the correct answer accurately captures the essence of amplitude in the context of wave properties.