- On a wave at sea, the trough is a point where the displacement of water is at 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.
- 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.
- Wavelength refers to a complete wave-cycle from crest to crest.
- Frequency refers to the number of wave-cycles that pass a given point in a given amount of time.
- The greater the distance from the top of a crest or to the bottom of a corresponding trough the more energy the wave carries.