From The Stargate Omnipedia
Point at which a vessel enters an open hyperspace window. It can be distinguished with a violent physical thrust which can potentially cause serious injury to an unsuspecting passenger. If one is unprepared the jolt can be thrown across a room.
Within the Serpent's Grasp - SG-1, save for Teal'c, is thrown about in a disordered and confused daze, receiving their first taste of hyperlaunch.