A material property is said to be isotropic if it does not depend upon direction. A similiar term is homogeity; a material property is said to be homogeneous if it does not depend upon position.
Isotropy and homogeneity often arise in material properties that depends on the microscpoic crystal structure of the material. Some of which I know include: elasticity and strain, electric susceptibility of dielectric materials (i.e. dielectric constant), the optical properties of some crystalline materials under the influence of an electric field (liquid crystals), as well as the electrical properties of some materials under a strong magnetic field (ferrites).