Final answer:
The number of wave crests or peaks in a light wave passing by a given point per unit of time is the frequency of the wave.
Step-by-step explanation:
The subject of this question is Physics. Specifically, it is related to the study of waves and their characteristics. In Physics, waves are described by their frequency, which is the number of wave cycles (crests or troughs) that pass a specific point in space per unit of time. This frequency can be measured in hertz (Hz), which represents the number of waves passing a given point in one second. So, in this case, the question is asking about the number of wave crests or peaks in a light wave passing by a given point per unit of time.