zero point

of a glass electrode
https://doi.org/10.1351/goldbook.Z06742
Value of the
pH
of a solution, which in combination with a stated outer
reference electrode
, gives zero emf from the operational cell.
Source:
PAC, 1985, 57, 531. (Definition of pH scales, standard reference values, measurement of pH and related terminology (Recommendations 1984)) on page 541 [Terms] [Paper]