A Crossing Drive is the engine a ship uses to travel at light speed or faster. It is standard on interstellar ships of all species.
A Crossing Drive generates a space-time bubble, allowing it to traverse space at a faster-than-light speed. It also generates some measure of protection against external space-time events, such as the Slate. It is analogous to the warp drive in Star Trek, Hyperdrive in Star Wars, or the Alcubierre drive in physics.