Z0
Symbol, Physics. Z-zero particle.
Dictionary.com Unabridged
Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019
Examples from the Web for z0
Z0 is the zenith distance of the moon's center midway through the hour of observation, that is, at the half hour.
A Quantitative Study of the Nocturnal Migration of Birds.|George H. Lowery.