Soaking
Soaking is a sexual practice of inserting the penis into the vagina but not subsequently thrusting or ejaculating. Soaking is reportedly used as a loophole with regards to premarital sex.
Soaking is sometimes accompanied by "jump humping", in which a third person is invited to bounce on the bed (or to push up on the mattress from below) for a couple engaged in soaking, thus generating motion for them.