Troughs: In transverse wave, the points where the particles of the medium have maximum displacement in the negative direction are called troughs. The lowest point of the wave is called the trough. In Figure, point C and G are troughs.
A trough is the opposite of a crest, so the minimum or lowest point in a cycle. A point on the wave is a trough if the displacement of the medium at that point is at a minimum. The trough of a wave is the point on the medium that exhibits the maximum amount of negative or downward displacement from the rest position.