Isn't it a sex lubricant?!
Joking aside, he wrote "z tube" which is quite simply just the plastic air inlet tube going to the throttle body as used on the 350Z. The G35 Skyline has a different air inlet pipe which is slightly more restrictive so the one from the 350Z is a good/cheap upgrade option for the G35/V35 owners.
Picture below: On the left is the 350Z air inlet tube & on the right is the G35 air inlet tube.