1. The transference of disease from one person to another (think "disease vector").
2. An illusion of self-motion.
If you're on a train and see an adjacent train moving, then you may have the feeling that the other train is stationary and you're actually the one who's moving, in the opposite direction. That's an example of linear vection.
Circular vection involves being at the center of a rotating drum (for example, stationary at the center of a merry-go-round).
Roll vection can occur when a person views something that is rotating around their line of sight...unfortunately, I'm having trouble thinking of a "real-world" example that doesn't involve an airplane in tailspin.
Vection can induce motion sickness.
Etymology: Latin vectio, to carry. Same base as convection.
I step away, unnoticed,
Unperceived; no shared warmth now.
Is no childhood game of watching you spin
Until we're both dizzy with laughter,
It is the transfer of control,
The transfer of departure.
A gift of power.
It is an easy thing to offer,
I didn't want it anyway.
Easy for you to accept,
Resenting every perception of its loss.
Where we stand now is unimportant,
All that matters is the widening gap;
All I want is for you to feel you've won.