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To be fair, both are 'waves' of some sort.

But, yeah, gravity waves are closer to the common understanding of the word 'waves'.

The current understanding of waves on a liquid surface is attributed to a clear boundary between two fluids with a density difference and a velocity gradient. Gravity plays no role in this.

Kelvin-Helmholtz instability: https://en.wikipedia.org/wiki/Kelvin%E2%80%93Helmholtz_insta...

Two fluids with a density difference and a velocity gradient usually have a common force acting upon them, e.g. gravity, which enforces so-said interface. Perturbations to the average interface are restored via this force, and these perturbations are called gravity waves.

KH Instabilities give rise to gravity waves.

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