The unit of stress is Nm-2 (Newtons per square meter), also known as Pascal (Pa). Stress is defined as force per unit area and is a measure of the internal forces acting on a material. When a force is applied to a material, it creates internal forces that tend to resist the deformation or change in shape. Stress is the measure of these internal forces per unit area. The unit Nm represents work or energy, while N represents force, and Nm2 does not have a physical meaning.