Stress

In engineering, Stress is a measure of the load applied for each unit of cross-sectional area of the material under load - i.e. Stress = Load / Area and is measured in newtons per square metre (Nm^-2).

When a material is subjected to stress it will deform in some way (e.g. be stretched or squashed) - although for many materials this may be only by a microscopically small amount. The resulting deformation is known as Strain and dividing Stress by Strain provides a measure of the stiffness of the material known as its Young's Modulus

Many terms in engineering, science and mathematics are represented by Greek symbols and Stress is allocated the symbol σ (sigma).