Shear stress
Is defined as the component of stress lying in the same plane with a material cross section. Shear stress arises from the force vector component similar to the cross section.
The formula to calculate average shear stress is:

where is
T = the shear stress;
F = the force applied;
A = the cross-sectional area of material with area parallel to the applied force vector.
Picture

Reference
(Stress shear)