No, it's "chuks."
Small "c" there.
Well, I have been in aviation for a while now and thought I knew most of the speed designations but this "Vz" threw me. Seriously, while we do have X, Y and Z axes, and those I know about, Vx and Vy have nothing to do with the X or Y axes so that this Vz business seems highly non-standard. ROC and ROD, rate of climb, rate of descent, that is understood by all so that I really think it's preferable.
Of course it is true that if one cannot dazzle with brilliance then to baffle with BS is a good alternative.