surface stress, \(T_{ij}\)

https://doi.org/10.1351/goldbook.S06191
The work required to form unit area of new surface by stretching under equilibrium conditions. It is numerically equal to the force acting in the jth direction per unit length of exposed edge, the edge being normal to the ith direction, that must be applied to a terminating surface to keep it in equilibrium, the ith and jth directions lying in the plane of the surface.
Source:
PAC, 1986, 58, 437. 'Interphases in systems of conducting phases (Recommendations 1985)' on page 451 (https://doi.org/10.1351/pac198658030437)