Plain English Meaning
The spinning mass of air shed from the wingtip on the side that the wind is blowing from. Because the wind pushes against it, this vortex tends to hang around near the runway instead of being blown clear.
Full Definition
The wingtip vortex generated on the wing positioned into the wind during a crosswind condition. In a crosswind, this vortex tends to remain near the runway surface and stay in place rather than drifting away, creating a wake turbulence hazard for following aircraft.
Context Anchor
Seen in discussions of induced drag, wingtip vortices, wake turbulence, and crosswind operations near a runway.