Stress is a fundamental concept in continuum mechanics. Stress can be thought of how a material responds to being applied by a force. In other words, materials do not “see” forces. They see stresses.
The magnitude of stress is proportional to the applied force, and inversely proportional to the area over which the force is applied. Stresses can be normal or shearing.
This page is part of The Encyclopedia of Stresses in Solids