In fluid dynamics, gravity waves are waves generated in a fluid medium or at the interface between two mediums (e.g. the atmosphere or ocean) which has the restoring force of gravity or buoyancy.

When a fluid parcel is displaced on an interface or internally to a region with a different density, gravity restores the parcel toward equilibrium resulting in an oscillation about the equilibrium state or wave orbit. Gravity waves on an air-sea interface are called surface gravity waves or surface waves while internal gravity waves are called internal waves. Ocean waves generated by wind are examples of gravity waves.

Wind waves, as their name suggests, are generated by wind transfering energy from the atmosphere to the oceans surface. At first capillary waves form on the ocean surface and grow in height at a linear rate propotional to the wind speed (as explained by Miles 1957; 1959). Once these small waves have formed they start to interact with the atmosphere through pressure differences and due to the ocean surface roughness - now the waves grow at rates which are exponentially proportional to the wind speed (as explained by Phillips 1957), producing larger and larger waves. This Miles-Phillips Mechanism process can continue until an equilibrim is reached, or until the wind stops transfering energy to the waves (i.e. blowing them along) or when they run out of ocean distance, also known as fetch length.

Gravity waves have a period of between 1 and 30 seconds (0.033 to 1 Hz). Alternatively, intragravity waves generally have a period between 30 seconds to 5 minutes (0.05 to 0.005 Hz). Infragravity waves can be felt rather than seen as they have a much greater wave energy.