In physics, a breaking wave is a wave whose amplitude reaches a critical level at which some process can suddenly start to occur that causes large amounts of wave energy to be dissipated.
At this point, simple physical models describing the dynamics of the wave will often become invalid, particularly those which assume linear behavior.
The most generally familiar sort of breaking wave is the breaking of water surface waves on a coastline.
Because of the horizontal component of the fluid velocity associated with the wave motion, wave crests steepen as the amplitude increases; wave breaking generally occurs where the amplitude reaches the point that the crest of the wave actually overturns - though the types of breaking water surface waves are discussed in more detail below.
Certain other effects in fluid dynamics have also been termed "breaking waves", partly by analogy with water surface waves.
In meteorology, gravity waves are said to break when the wave produces regions where the potential temperature decreases with height, leading to energy dissipation through convective instability; likewise Rossby waves are said to break when the potential vorticity gradient is overturned.
Wave breaking also occurs in plasmas, when the particle velocities exceed the wave's phase speed.