1. The movement in a gas or liquid in which the hotter parts move upward and the colder elements go down: The chemist explained that convection consists of "circulatory movements" that are related to the rising of the warmer, less dense particles; and the sinking of cooler, more dense particles.
2. Etymology: from Late Latin convectio which comes from convehere, "to carry, to bring together".

The vertical movement of a layer of water caused by changes in the temperature-salinity relationship resulting in it becoming heavier than the water below it: Thermohaline convection is a kind of hydrodynamic instability and arrises due to one layer becoming colder or more saline, or both, and thus more dense.