What does this wiring schematic symbol mean?

That's showing the internal workings of a typical USB cable. The shield (top line) is connected to the chassis of both devices. USB Data- and USB Data+ are twisted together for better noise rejection, at the cost of increased capacitance between the two. Likewise, power (VBUS) and ground are twisted for the same reason.

The crossed wires means that the cable must be a "Twisted pair".

Additionally, the dotted line indicates an RF shield (e.g. metal foil or braid).