If we imagine a force acting on a block, F, which is resting on the floor. The floor exerts an equal and opposite force back on the block. If this didn’t happen the block would move.
This force acts on sections through the block parallel to the top surface, and the block is said to be in a state of stress.
The intensity of the stress, σ, is determined by the force divided by the area of the block surface, so:
This particular stress is called a tensile stress because the force is acting outwards at right angles to the block surface.