In certain circumstances, one may measure surface tensions that are different from the equilibrium value. Such a surface tension is called the dynamic surface (or interfacial) tension (γ dyn or σ dyn). The equilibrium value is then called the static surface (or interfacial) tension (γ st or σ st). The modifying signs may be omitted if there is no danger of ambiguity.
PAC, 1972, 31, 577. 'Manual of Symbols and Terminology for Physicochemical Quantities and Units, Appendix II: Definitions, Terminology and Symbols in Colloid and Surface Chemistry' on page 597 (https://doi.org/10.1351/pac197231040577)