The crest is the highest point of a wave, where the displacement of the medium is at its maximum.
Topic 6.1: 6.1 Waves
Crest cheat sheet for homework
The trough is the lowest point of a wave, where the displacement of the medium is at its minimum.
The amplitude is the maximum displacement from equilibrium in a wave.
The wavelength is the distance between two consecutive crests or troughs in a wave.