Jamjuice

(Sigh) You can lead a horse to water.... lol

Condensation or contrails. The example many teachers use is a boiling kettle. Just above the opening of the kettle, nothing is visible, (water vapour) but a little bit higher..... steam is seen rising, (vapour has cooled and condensed into a visible cloud of steam).

Not in the aviation world I know. I work for a large flight training academy, (over 80 cfi's) teaching the next generation of airline pilots. They should know the difference between vapour and liquid water after their first week of ground school!

I hate to be "that guy" but..... It's not vapor you're seeing behind the Hornet. Water vapor is the gaseous form of water and is invisible to human eyes. What you're seeing is tiny droplets of liquid water, (just like clouds) condensing out of the air. This happens because the wings cause a large drop in pressure. If pressure drops, temperature also drops and if the temperature drops below the current dew point... condensation will occur.