Answer:
Frequency
Explanation:
When we talk about crests, we are referring to the high points of a wave.
We measure wave frequency by counting out the the number of crests (or high points) of a given wave that pass by a given point in a set amount of time. Thus, the higher the number of crests, the greater the frequency of the wave and vice versa.
We define the frequency of a wave as the number of waves that passes by a fixed point within a given period of time.
