Isotropic tangent modulus

Hi,


I have in my model material nonlinearity and contact nonlinearity, because I connect 3-4 components together. Thus I have to specify the plasticity under solid mechanics - Linear Elastic Material. If I do this, I need more material properties, as for example the isotropic tangent modulus.
What is this isotropic tangent modulus and how do I determine it? What impact this module has on the model?

Many Thanks.