But liquids aren’t the only entrainers. Gases can also entrain each other. In fluid dynamics and related fields (including meteorology), entrainment refers to a turbulent fluid flow affecting a second fluid flow. In other words, when a turbulent flow is adjacent to a less turbulent flow, the turbulent flow will advance into the less turbulent flow, entraining it and making it more turbulent. Note that this is not a ‘jet’ of fluid hitting a stagnant ‘pool’ of fluid, but simply one flow passing adjacent to another flow (or stagnant layer). In meteorology this accounts for the mixing of otherwise discreet airflows, which can often mix humid and dry air masses.
Read all the other possible meanings on Everything2
and the media: