OK, thank you for the information. I think that the term, generally, means: when we intend to model a particular body or structure, should we assume that the material is elastic, or plastic, or incompressible elastic (like rubber - this is a special case for FEA and may require using hybrid models, when both displacements and stresses appear in the vector of unknown variables), etc. Other specific features may (or should) also be taken into account: the material may be not isotropic, but orthotropic, or even have some general anisotropic properties. The material may or may not manifest fatigue, depending on the actual loading conditions, etc. So there is a huge variety of different material properties and models that are to be taken into account when the engineer is building a particular FEA model.