Z bench: The resulting Z when all defects are moved into one tail of the distribution (PPM<LSL + PPM>USL) expressed as either long term or short term depending on the PPM values used in the calculation.
Zero defects: A performance standard and methodology developed by Philip B. Crosby that states if people commit themselves to watching details and avoiding errors, they can move closer to the goal of zero.
Z shift: Z shift is the difference between ZST and ZLT. The larger the Z shift, the more you are able to improve the control of the special factors identified in the subgroups. - or - Difference between short-term and long-term Z bench.