The ratio of stress to rate of
strain, calculated from measurements of forces and velocities as though the liquid were Newtonian. If the liquid is actually non-Newtonian, the apparent
viscosity depends on the type and dimensions of the apparatus used.
Source:
PAC, 1979, 51, 1213
(Manual of symbols and terminology for physicochemical quantities and units. Appendix II: Definitions, terminology and symbols in colloid and surface chemistry. Part 1.13. Selected definitions, terminology and symbols for rheological properties)
on page 1217