The resultant vector d F / d S {\displaystyle d\mathbf {F} /dS} is defined as the surface traction,[1] also called stress vector,[2] traction,[3] or traction vector.[4] given by T ( n ) = T i ( n ) e i {\displaystyle \mathbf {T} ^{(\mathbf {n} )}=T_{i}^{(\mathbf {n} )}\mathbf {e} _{i}} at the point P {\displaystyle P} associated with a plane with a normal vector n {\displaystyle \mathbf {n} } :