Wave height is the vertical difference between the wave through and the wave crest.
The wave field is a combination of waves of different height, length and directions and the significant wave height is a useful way to describe the sea state. It has been defined to approximate the wave heights visually estimated by experienced mariners.
The significant wave height is calculated from the energy spectrum of the measured waves. The wave spectrum tells how the energy is distributed to different wave lengths and directions.
The significant wave height corresponds also the average of one third of the highest waves in a measured wave record.
The highest individual wave in a wave field can be nearly two times higher than the significant wave height. The reported highest individual waves are not based on direct measurement, but are statistically estimated from the significant wave height.