A trough is the point on a wave with the maximum value of downward displacement within a wave-cycle. A crest is the opposite of a trough, so the maximum or highest point in a wave-cycle.
- On a wave at sea, the trough is a point where the displacement of water reaches a minimum. A crest is the opposite of a trough, so a crest is a point where the displacement of the water is at a maximum.
- In the case of an electromagnetic wave which has an electric and a magnetic axis, a trough on either axis refers to minimum displacement in the negative direction whilst a crest refers to maximum displacement.
- Wavelength refers to a complete wave-cycle from one crest to the next, or one trough to the next.
- Frequency refers to the number of wave-cycles that pass a given point in a given amount of time.
- The amplitude of a wave is a measurement of the distance from the centre line (or the still position) to the top of a crest or to the bottom of a corresponding trough.
- Amplitude is related to the energy a wave carries. The energy a wave carries is related to frequency and amplitude. The higher the frequency, the more energy, and the higher the amplitude, the more energy.