fluid

An extreme version of vorticity is a vortex. The vortex is a spinning, cyclonic mass of fluid, which can be observed in the rotation of water going down a drain, as well as in smoke rings, tornados and hurricanes.

fluid inclusion Petrology, a tiny fluid- or gas-filled cavity in an igneous rock. 1-100 micrometers in diameter, formed by the entrapment of a fluid, typically that from which the rock crystallized.