yield stress

The shear stressσ 0 or τ 0 at which yielding starts abruptly. Its value depends on the criterion used to determine when yielding occurs.
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