Finite deformation is a branch of mechanics that deals with the behavior of materials under large deformations and strains. Unlike small deformation theory, which assumes that the deformation is small enough for linear elastic behavior to be applicable, finite deformation theory considers large deformations that result in changes to the material's structure and properties. This area of research is particularly important for studying the behavior of materials under extreme conditions such as high stress, high strain, or high temperature. Finite deformation theory is used in various fields including solid mechanics, fluid dynamics, and biomechanics.