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While making love to a woman from behind, rather than reaching under her arms to fondle her breasts, the partner reaches over her shoulders.

May be performed standing or sitting, or in a motor vehicle.
Jack and Jill usually carseat while making love. She says it is off the hook.
by Carseater March 27, 2010
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2
Putting a girls driver seat all the way down and back, while sitting naked under her, having sex while she drives
She crashed her car while we were on our way to a trampoline park because we were doing the car seat.
by CJK5 May 24, 2018
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