"Gravity waves" are ordinary water waves, or other waves of a fluid, where gravity provides the restoring force:

https://en.wikipedia.org/wiki/Gravity_wave

They have absolutely nothing to do with gravitational waves.

Nonetheless, in the gravitational wave community (i.e. LIGO) we don't usually ever talk about true "gravity waves" so we use the terms interchangably.

The exception is that "gravity waves" in the Earth and the atmosphere can couple to LIGO through ordinary Newtonian gravity, which is something we have to think about and exclude.