Z-axis
The Z-axis was a line representing the depth of a movement.
In 2154, Trip Tucker told Travis Mayweather to fly a Xindi-Insectoid assault shuttle "negative z axis ten degrees". (ENT: "Azati Prime")
Later that year, T'Pol ordered Mayweather to turn "eighty degrees z axis". (ENT: "The Council")
In 2374, Tim Watters ordered the helmsman of the USS Valiant to "plot an escape course down the z axis." (DS9: "Valiant")