Final Answer:
The hollow of the fingerwave may be described by the term "trough."
Step-by-step explanation:
In hairstyling, particularly when creating finger waves, the hollow or low point between the waves is commonly referred to as the "trough." The term "trough" is used to describe the concave or recessed area that forms between the crest (peak) of one wave and the crest of the adjacent wave. This term is aptly employed to capture the specific structure and appearance of the hairstyle.
The other options provided, such as "pinnacle," "crescent," "zenith," "apex," and "nadir," do not accurately represent the characteristic features of the hollow in a fingerwave.