What is the highest part of a wave called?

The highest part of the wave is called the crest. The lowest part is called the trough. The wave height is the overall vertical change in height between the crest and the trough and the distance between two successive crests (or troughs) is the length of the wave or wavelength. While one normally associates an up-and-down motion with the passage of each wave. Actually, a circular motion occurs. It is this orbital motion of the water (or objects on the surface of the water) that causes an object to bob up and down, forward and backward as waves pass under it.

Source: National Weather Service