1. The transportation of a mass of matter and its conserved properties, like energy, by motion: Examples of advection can be seen in the movement of pollutants or silt in a stream or river which flows downstream.
2. The conveyance of an atmospheric property caused by the horizontal movement of air: The transfer of heat, humidity or moisture, or salinity, which are some properties carried through the motion of the air, is known as advection.
3. The horizontal movement of water, as in an ocean current: Advection is important for the precipitation of rain, snow, etc. from clouds, or for the formation of shaping of such orographic clouds.