The
shear stress
or

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