What is the term for the low area between two waves?

The term for the low area between two waves is "trough." In the context of ocean waves, the trough refers specifically to the lowest point of the wave cycle, where the water level dips down between the two peaks (crests) of the waves. Identifying the trough is essential for understanding wave behavior, as it is one of the key features that define wave characteristics such as wave height and frequency.

The other terms presented do not accurately describe this specific feature of waves. A "valley" typically refers to a low area on land, not a characteristic of wave formation. A "tube" often refers to formations that can occur in waves, such as when a wave breaks and creates a cylindrical shape, but it does not indicate the area between two waves. A "depression," while it may imply a low area, does not have a specific application in wave terminology like the term "trough" does. Thus, using "trough" is the precise and correct way to describe the low point between the two waves.