What is elastic modulus?

In a tensile test, a specimen of material is pulled apart slowly until it breaks. Measurement is continuously taken of the increase in length and the force applied. The increase in length is normalized by dividing it by the original length, and the force is converted to stress by dividing it by the original cross-section area of the specimen. The results are plotted on a graph, called a stress-strain curve, with the stress on the Y axis and the strain on the X axis. The initial part of the curve is usually linear. That linear section is called the elastic region. The slope of the line in that area, which is stress divided by strain in the elastic region, is the elastic modulus.