In physics, the mechanical tension is a force exerted on a unit area. The mechanical tension is formed by normal and tangential components to the surface (for example in the case of cutting and/or torsion). For the fluids, the analogous concept of pressure is defined (in the case of the normal component).
In geology, the term “tension” refers to stress which stretches rocks in two opposite directions. The rocks become longer in a lateral direction and thinner in a vertical direction. One important result of tensile stress is jointing in rocks. However, tensile stress is rare because most subsurface stress is compressive, due to the weight of the overburden.