Inertial gravity waves
Gravity waves in a rotating system are called inertial gravity waves. They are also often called just "gravity waves".
In gravity waves in a stationary system (a non-rotating system), the particles of the fluid oscillate on a vertical plane parallel to the direction of the waves. When Coriolis' force acts on the waves, the particles oscillate in an elliptical locus. In a rotating system, Coriolis' force also adds to the restitutive force acting on the waves, so compared to an inertial system, waves in a rotating system with the same wavelength have a shorter period.
In a stationary system, as the wavelength becomes longer, the period of the wave becomes infinitely longer, however in a rotating system, the period of the wave does not become longer than the inertial period, and at an infinite wavelength, inertial oscillation occurs.