Strains, or tensions, refer to the internal forces that develop within materials when they are subjected to external loads. These forces can cause deformation, which is the change in shape or size of the material. Strains are typically measured as a ratio of the change in length to the original length, and they can be classified into different types, such as tensile strain, compressive strain, and shear strain. Understanding strains is crucial in fields like engineering and materials science, as it helps predict how materials will behave under various conditions. By analyzing strains, engineers can design structures and components that can withstand applied forces without failing, ensuring safety and reliability in applications ranging from bridges to buildings.